A professional wrestling match can end in a draw. A draw occurs if both opponents are simultaneously disqualified (as via countout or if the referee loses complete control of the match and both opponents attack each other with no regard to being in a match, like Brock Lesnar vs. Undertaker at Unforgiven in 2002), neither opponent is able to answer a ten-count, or both opponents simultaneously win the match. The latter can occur if, for example, one opponent's shoulders touch the mat while maintaining a submission hold against another opponent. If the opponent in the hold begins to tap out at the same time a referee counts to three for pinning the opponent delivering the hold, both opponents have legally achieved scoring conditions simultaneously. Traditionally, a championship may not change hands in the event of a draw (though it may become vacant), though some promotions such as TNA have endorsed rules where the champion may lose a title by disqualification. A variant of the draw is the time-limit draw, where the match does not have a winner by a specified time period (a one-hour draw, which was once common, is known in wrestling circles as a "Broadway").


A wrestling match may be declared a no contest if the winning conditions are unable to occur. This can be due to excessive interference, loss of referee's control over the match, one or more participants sustaining debilitating injury not caused by the opponent, or the inability of a scheduled match to even begin. A no contest is a state separate and distinct from a draw — a draw indicates winning conditions were met. Although the terms are sometimes used interchangeably in practice, this usage is technically incorrect.


While each wrestling match is ostensibly a competition of athletics and strategy, the goal of each match from a business standpoint is to excite and entertain the audience. Although the competition is staged, dramatic emphasis can be utilized to draw out the most intense reaction from the audience. Heightened interest results in higher attendance rates, increased ticket sales, higher ratings on television broadcasts (which result in greater ad revenue), higher pay-per-view buyrates, and sales of branded merchandise and recorded video footage. All of these contribute to the profit of the promotion company.


In Latin America and English-speaking countries, most wrestlers (and other on-stage performers) portray character roles, sometimes with personalities wildly different from their own. These personalities are a gimmick intended to heighten interest in a wrestler without regard to athletic ability. Some can be unrealistic and cartoon-like (such as Doink the Clown), while others carry more verisimilitude and can be seen as exaggerated versions of the performer's real life personality (such as Chris Jericho, The Rock, John Cena, Stone Cold Steve Austin, and CM Punk). In lucha libre, many characters wear masks, adopting a secret identity akin to a superhero, a near-sacred tradition.


An individual wrestler may sometimes use their real name, or a minor variation of it, for much of their career, such as Angelo Poffo, Ernie Ladd, Verne Gagne, Bret Hart, and Randy Orton. Others can keep one ring name for their entire career (cases in point include Chris Jericho, Shawn Michaels, CM Punk and Ricky Steamboat), or may change from time to time to better suit the demands of the audience or company. Sometimes a character is owned and trademarked by the company, forcing the wrestler to find a new one when they leave (although a simple typeset change, such as changing Rhyno to Rhino, can usually get around this), and sometimes a character is owned by the wrestler. Sometimes, a wrestler may change their legal name in order to obtain ownership of their ring name (examples include Andrew Martin and Warrior). Many wrestlers (such as The Rock and The Undertaker) are strongly identified with their character, even responding to the name in public or between friends. It's actually considered proper decorum for fellow wrestlers to refer to each other by their stage names/characters rather than their birth/legal names, unless otherwise introduced. A professional wrestling character's popularity can grow to the point that it makes appearances in other media (see Hulk Hogan and El Santo) or even give the performer enough visibility to enter politics (Antonio Inoki and Jesse Ventura, among others).


Typically, matches are staged between a protagonist (historically an audience favorite, known as a babyface, or "the good guy") and an antagonist (historically a villain with arrogance, a tendency to break rules, or other unlikable qualities, called a heel). In recent years, however, antiheroes have also become prominent in professional wrestling. There is also a less common role of a "tweener", who is neither fully face nor fully heel yet able to play either role effectively (case in point, Samoa Joe during his first run in TNA from June 2005 to November 2006).


At times a character may "turn", altering their face/heel alignment. This may be an abrupt, surprising event, or it may slowly build up over time. It almost always is accomplished with a markable change in behavior on the part of the character. Some turns become defining points in a wrestler's career, as was the case when Hulk Hogan turned heel after being a top face for over a decade. Others may have no noticeable effect on the character's status. If a character repeatedly switches between being a face and heel, this lessens the effect of such turns, and may result in apathy from the audience. Vince McMahon is a good example of having more heel and face turns than anyone in WWE history.


As with personae in general, a character's face or heel alignment may change with time, or remain constant over its lifetime (the most famous example of the latter is Ricky Steamboat, a WWE Hall of Famer who remained a babyface throughout his entire career). Sometimes a character's heel turn will become so popular that eventually the audience response will alter the character's heel-face cycle to the point where the heel persona will, in practice, become a face persona, and what was previously the face persona, will turn into the heel persona, such as when Dwayne Johnson first began using "The Rock" persona as a heel character, as opposed to his original "Rocky Maivia" babyface persona. Another legendary example is Stone Cold Steve Austin, who was originally booked as a heel, with such mannerisms as drinking on the job, using profanity, breaking company property, and even breaking into people's private homes. However, much to WWF's surprise, the fans enjoyed Austin's antics so much that he became one of the greatest antiheroes in the history of the business. He, along with the stable of D-Generation X, is generally credited with ushering in the Attitude Era of WWF programming.


In some cases a wrestler may possess admirable physical traits but perceived mediocre public speaking abilities (such as Brock Lesnar), or their gimmick may be that of a "wild savage" needing a handler (such as Kamala). Such performers have historically employed a manager, who speaks on their behalf and adds to the performance. Managers have sometimes become major personalities, including Bobby Heenan, Paul Heyman, Ernie Roth, and Paul Bearer. A manager role may also be filled by a "valet", typically an appealing female who may participate in love triangle storylines, "damsel in distress" situations, and scripted fights with female wrestlers. Some of these have also gone on to become recognized stars, such as Tammy Lynn Sytch, Stacy Keibler, and Miss Elizabeth.


While true exhibition matches are not uncommon, most matches tell a story analogous to a scene in a play or film, or an episode of a serial drama: The face will sometimes win (triumph) or sometimes lose (tragedy). Longer story arcs can result from multiple matches over the course of time. Since most promotions have a championship title, competition for the championship is a common impetus for stories. Also, anything from a character's own hair to their job with the promotion can be wagered in a match. The same type of good vs. evil storylines were also once popular in roller derby.


Other stories result from a natural rivalry between two or more characters. Outside of performance, these are referred to as feuds. A feud can exist between any number of participants and can last for a few days up to multiple decades. The feud between Ric Flair and Ricky Steamboat lasted from the late 1970s into the early 1990s and allegedly spanned over two thousand matches (although most of those matches were mere dark matches). The career-spanning history between characters Mike Awesome and Masato Tanaka is another example of a long-running feud, as is the case of Stone Cold Steve Austin vs. Mr. McMahon, one of the most lucrative feuds in the World Wrestling Federation (WWF) during 1998 and 1999.


Also, anything that can be used as an element of drama can exist in professional wrestling stories: romantic relationships (including love triangles and marriage), racism, classism, nepotism, favoritism, corporate corruption, family bonds, personal histories, grudges, theft, cheating, assault, betrayal, bribery, seduction, stalking, confidence tricks, extortion, blackmail, substance abuse, self-doubt, self-sacrifice; even kidnapping, sexual fetishism, necrophilia, misogyny, rape and death have been portrayed in wrestling. Some promotions have included supernatural elements such as magic, curses, the undead and Satanic imagery (most notably The Undertaker and his Ministry of Darkness, a stable that regularly performed evil rituals and human sacrifice in Satanic-like worship of a hidden power figure). Celebrities would also be involved in storylines.


Behind the scenes, the bookers in a company will place the title on the most accomplished performer, or those the bookers believe will generate fan interest in terms of event attendance and television viewership. Lower ranked titles may also be used on the performers who show potential, thus allowing them greater exposure to the audience. However other circumstances may also determine the use of a championship. A combination of a championship's lineage, the caliber of performers as champion, and the frequency and manner of title changes, dictates the audience's perception of the title's quality, significance and reputation.


A wrestler's championship accomplishments can be central to their career, becoming a measure of their performance ability and drawing power. In general, a wrestler with multiple title reigns or an extended title reign is indicative of a wrestler's ability to maintain audience interest and/or a wrestler's ability to perform in the ring. As such, the most accomplished or decorated wrestlers tend to be revered as legends despite the predetermined nature of title reigns. American wrestler Ric Flair has had multiple world heavyweight championship reigns spanning over three decades. Japanese wrestler Último Dragón once held and defended a record 10 titles simultaneously.


All notable wrestlers now enter the ring accompanied by music, and regularly add other elements to their entrance. The music played during the ring entrance will usually mirror the wrestler's personality. Many wrestlers, particularly in America, have music and lyrics specially written for their ring entrance. While invented long before, the practice of including music with the entrance gained rapid popularity during the 1980s, largely as a result of the huge success of Hulk Hogan and the WWF, and their Rock 'n' Wrestling Connection. When a match is won, the victor's theme music is usually also played in celebration.


The women's division of professional wrestling has maintained a recognized world champion since 1937, when Mildred Burke won the original World Women's title. She then formed the World Women's Wrestling Association in the early 1950s and recognized herself as the first champion, although the championship would be vacated upon her retirement in 1956. The NWA, however, ceased to acknowledge Burke as their Women's World champion in 1954, and instead acknowledged June Byers as champion after a controversial finish to a high-profile match between Burke and Byers that year. Upon Byers' retirement in 1964, The Fabulous Moolah, who won a junior heavyweight version of the NWA World Women's Championship (the predecessor to the WWE's Women's Championship) in a tournament back in 1958, was recognized by most NWA promoters as champion by default.


In Japan, professional wrestling done by female wrestlers is called joshi puroresu (女子プロレス) or joshi puro for short. Female wrestling is usually handled by promotions that specialize in joshi puroresu rather than divisions of otherwise male-dominated promotions, as is the case in the United States. However, joshi puroresu promotions usually have agreements with male puroresu promotions such that they recognize each other's titles as legitimate, and may share cards. All Japan Women's Pro-Wrestling was the dominant joshi organization from the 1970s to the 1990s.


In the 1980s, mixed tag team matches began to take place, with a male and female on each team and a rule stating that each wrestler could only attack the opponent of the same gender. If a tag was made, the other team had to automatically switch their legal wrestler as well. Despite these restrictions, many mixed tag matches do feature some physical interaction between participants of different genders. For example, a heel may take a cheap shot at the female wrestler of the opposing team to draw a negative crowd reaction. In lucha libre, cheap-shots and male-female attacks are not uncommon.


Intergender singles bouts were first fought on a national level in the 1990s. This began with Luna Vachon, who faced men in ECW and WWF. Later, Chyna became the first female to hold a belt that was not exclusive to women when she won the Intercontinental Championship. While it is a rare feat in WWE, in TNA, ODB participates in singles intergender matches. Also, ODB's kayfabe husband and tag team partner Eric Young held the Knockouts Tag Team Championship for a record 478 days before it was stripped by Brooke Hogan because Young was a male.


Some wrestlers may have their own specific "mini me", like Mascarita Sagrada, Alebrije has Quije, etc. There are also cases in which midgets can become valets for a wrestler, and even get physically involved in matches, like Alushe, who often accompanies Tinieblas, or KeMonito, who is portrayed as Consejo Mundial de Lucha Libre's mascot and is also a valet for Mistico. Dave Finlay was often aided in his matches by a midget known mainly as Hornswoggle while in WWE, who hid under the ring and gave a shillelagh to Finlay to use on his opponent. Finlay also occasionally threw him at his opponent(s). Hornswoggle has also been given a run with the Cruiserweight Championship and feuded with D-Generation X in 2009.


Though they have not had the level of exposure as other wrestlers, bears have long been a part of professional wrestling. Usually declawed and muzzled, they often wrestled shoot matches against audience members, offered a cash reward if they could pin the bear. They also wrestled professionals in worked, often battle royal or handicap, matches (usually booked so the bear won). Though they have wrestled around the world and continue to do so, wrestling bears enjoyed their greatest popularity in the Southern United States, during the 1960s and 1970s. The practice of bear wrestling has met strong opposition from animal rights activists in recent decades, contributing to its lack of mainstream acceptance. As of 2006, it is banned in 20 U.S. states. Perhaps the most famous wrestling bears are Ginger, Victor, Hercules and Terrible Ted.


Professional wrestling in the U.S. tends to have a heavy focus on story building and the establishment of characters (and their personalities). There is a story for each match, and even a longer story for successive matches. The stories usually contain characters like faces and heels, and less often antiheroes and tweeners. It is a "triumph" if the face wins, while it is a "tragedy" if the heel wins. The characters usually have strong and sharp personalities, with examples like Doink the Clown, whose personality is melodramatic, slapstick and fantastical. The opposition between faces and heels is very intense in the story, and the heels may even attack the faces during TV interviews. The relationship between different characters can also be very complex.


Although professional wrestling in Mexico (lucha libre) also has stories and characters, they are less emphasized. Wrestlers in Mexico are traditionally more agile and perform more aerial maneuvers than professional wrestlers in the U.S. who, more often, rely on power moves and strikes to subdue their opponents. The difference in styles is due to the independent evolution of the sport in Mexico beginning in the 1930s and the fact that wrestlers in the cruiserweight division (peso semicompleto) are often the most popular wrestlers in Mexican lucha libre. Wrestlers often execute high flying moves characteristic of lucha libre by utilizing the wrestling ring's ropes to catapult themselves towards their opponents, using intricate combinations in rapid-fire succession, and applying complex submission holds. Lucha libre is also known for its tag team wrestling matches, in which the teams are often made up of three members, instead of two as is common in the U.S.


The style of Japanese professional wrestling (puroresu) is again different. With its origins in traditional American style of wrestling and still being under the same genre, it has become an entity in itself. Despite the similarity to its American counterpart in that the outcome of the matches remains predetermined, the phenomena are different in the form of the psychology and presentation of the sport; it is treated as a full contact combat sport as it mixes hard hitting martial arts strikes with shoot style submission holds, while in the U.S. it is rather more regarded as an entertainment show. Wrestlers incorporate kicks and strikes from martial arts disciplines, and a strong emphasis is placed on submission wrestling, and unlike the use of involved storylines in the U.S., they are not as intricate in Japan, more emphasis is placed on the concept of Fighting Spirit, meaning the Wrestlers display of physical and mental stamina are valued a lot more than theatrics. Many of Japan's wrestlers including top stars such as Shinya Hashimoto, Riki Choshu and Keiji Mutoh came from a legitimate martial arts background and many Japanese wrestlers in the 1990s began to pursue careers in mixed martial arts organizations such as Pancrase and Shooto which at the time retained the original look of puroresu, but were actual competitions.


Those involved in producing professional wrestling have developed a kind of global fraternity, with familial bonds, shared language and passed-down traditions. New performers are expected to "pay their dues" for a few years by working in lower-profile promotions and working as ring crew before working their way upward. The permanent rosters of most promotions develop a backstage pecking order, with veterans mediating conflicts and mentoring younger wrestlers. For many decades (and still to a lesser extent today), performers were expected to keep the illusions of wrestling's legitimacy alive even while not performing, essentially acting in character any time they were in public. Some veterans speak of a "sickness" among wrestling performers, an inexplicable pull to remain active in the wrestling world despite the devastating effects the job can have on one's life and health.


Fans of professional wrestling have their own subculture, comparable to those of science fiction, video games, or comic books (in some cases, the "fandoms" overlap; in recent years, some professional wrestlers, particularly those who nurture an anti-establishment rebel persona, such as CM Punk, have made guest appearances at comic book conventions). Those who are interested in the backstage occurrences, future storylines, and reasonings behind company decisions read newsletters written by journalists with inside ties to the wrestling industry. These "rags" or "dirt sheets" have expanded into the Internet, where their information can be dispensed on an up-to-the-minute basis. Some have expanded into radio shows.


Some fans enjoy a pastime of collecting tapes of wrestling shows from specific companies, of certain wrestlers, or of specific genres. The Internet has given fans exposure to worldwide variations of wrestling they would be unable to see otherwise. Since the 1990s, many companies have been founded which deal primarily in wrestling footage. When the WWF purchased both WCW and ECW in 2001, they also obtained the entire past video libraries of both productions and have released many past matches online and on home video.


From the first established world championship, the top professional wrestlers have garnered fame within mainstream society. Each successive generation has produced a number of wrestlers who extend their careers into the realms of music, acting, writing, business, politics or public speaking, and are known to those who are unfamiliar with wrestling in general. Conversely, celebrities from other sports or general pop culture also become involved with wrestling for brief periods of time. A prime example of this is The Rock 'n' Wrestling Connection of the 1980s, which combined wrestling with MTV.


Many television shows and films have been produced which portray in-character professional wrestlers as protagonists, such as Ready to Rumble, ¡Mucha Lucha!, Nacho Libre, and the Santo film series. In the wildly popular Rocky series of films about the fictional boxer Rocky Balboa, Rocky III saw its hero fighting a "boxer vs. wrestler" exhibition match against the enormous and villainous wrestler "Thunderlips", portrayed by real-life soon-to-be wrestling icon Hulk Hogan. At least two stage plays set in the world of pro wrestling have been produced: The Baron is a comedy that retells the life of an actual performer known as Baron von Raschke. From Parts Unknown... is an award-nominated Canadian drama about the rise and fall of a fictional wrestler. The 2009 South Park episode "W.T.F." played on the soap operatic elements of professional wrestling. One of the lead characters on the Disney Channel series Kim Possible was a huge fan of pro wrestling and actually featured it on an episode (with two former WWE wrestlers voicing the two fictitious wrestlers featured in the episode). The 2008 film The Wrestler, about a washed-up professional wrestler, garnered several Oscar nominations.


With its growing popularity, professional wrestling has attracted attention as a subject of serious academic study and journalistic criticism. Many courses, theses, essays, and dissertations have analyzed wrestling's conventions, content, and its role in modern society. It is often included as part of studies on theatre, sociology, performance, and media. The Massachusetts Institute of Technology developed a course of study on the cultural significance of professional wrestling, and anthropologist Heather Levi has written an ethnography about the culture of lucha libre in Mexico.


However, this was not always the case; in the early 20th century, once it became apparent that the "sport" was worked, pro wrestling was looked down on as a cheap entertainment for the uneducated working class — an attitude that still exists to varying degrees today. The French theorist Roland Barthes was among the first to propose that wrestling was worthy of deeper analysis, in his essay "The World of Wrestling" from his book Mythologies, first published in 1957. Barthes argued that it should be looked at not as a scamming of the ignorant, but as spectacle; a mode of theatric performance for a willing, if bloodthirsty, audience. Wrestling is described as performed art which demands an immediate reading of the juxtaposed meanings. The logical conclusion is given least importance over the theatrical performers of the wrestlers and the referee. According to Barthes, the function of a wrestler is not to win: it is to go exactly through the motions which are expected of them and to give the audience a theatrical spectacle. This work is considered a foundation of all later study.


While pro wrestling is often described simplistically as a "soap opera for males", it has also been cited as filling the role of past forms of literature and theatre; a synthesis of classical heroics, commedia dell'arte, revenge tragedies, morality plays, and burlesque. The characters and storylines portrayed by a successful promotion are seen to reflect the current mood, attitudes, and concerns of that promotion's society (and can, in turn, influence those same things). Wrestling's high levels of violence and masculinity make it a vicarious outlet for aggression during peacetime.


Documentary filmmakers have studied the lives of wrestlers and the effects the profession has on them and their families. The 1999 theatrical documentary Beyond the Mat focused on Terry Funk, a wrestler nearing retirement; Mick Foley, a wrestler within his prime; Jake Roberts, a former star fallen from grace; and a school of wrestling student trying to break into the business. The 2005 release Lipstick and Dynamite, Piss and Vinegar: The First Ladies of Wrestling chronicled the development of women's wrestling throughout the 20th century. Pro wrestling has been featured several times on HBO's Real Sports with Bryant Gumbel. MTV's documentary series True Life featured two episodes titled "I'm a Professional Wrestler" and "I Want to Be a Professional Wrestler". Other documentaries have been produced by The Learning Channel (The Secret World of Professional Wrestling) and A&E (Hitman Hart: Wrestling with Shadows). Bloodstained Memoirs explored the careers of several pro wrestlers, including Chris Jericho, Rob Van Dam and Roddy Piper.


Although professional wrestling is worked, there is a high chance of injury, and even death. Strikes are often stiff, especially in Japan and in independent wrestling promotions such as Combat Zone Wrestling (CZW) and Ring of Honor (ROH). The ring is often made out of 2 by 8 timber planks. Many of the injuries that occur in pro wrestling are shoulders, knee, back, neck, and rib injuries. Chronic traumatic encephalopathy and traumatic brain injuries have also been linked to pro wrestling, including in the double-murder suicide case involving Chris Benoit. Professional wrestler Davey Richards said in 2015, "We train to take damage, we know we are going to take damage and we accept that".


Relatively insensitive film, with a correspondingly lower speed index, requires more exposure to light to produce the same image density as a more sensitive film, and is thus commonly termed a slow film. Highly sensitive films are correspondingly termed fast films. In both digital and film photography, the reduction of exposure corresponding to use of higher sensitivities generally leads to reduced image quality (via coarser film grain or higher image noise of other types). In short, the higher the sensitivity, the grainier the image will be. Ultimately sensitivity is limited by the quantum efficiency of the film or sensor.


The Warnerke Standard Sensitometer consisted of a frame holding an opaque screen with an array of typically 25 numbered, gradually pigmented squares brought into contact with the photographic plate during a timed test exposure under a phosphorescent tablet excited before by the light of a burning Magnesium ribbon. The speed of the emulsion was then expressed in 'degrees' Warnerke (sometimes seen as Warn. or °W.) corresponding with the last number visible on the exposed plate after development and fixation. Each number represented an increase of 1/3 in speed, typical plate speeds were between 10° and 25° Warnerke at the time.


The Scheinergrade (Sch.) system was devised by the German astronomer Julius Scheiner (1858–1913) in 1894 originally as a method of comparing the speeds of plates used for astronomical photography. Scheiner's system rated the speed of a plate by the least exposure to produce a visible darkening upon development. Speed was expressed in degrees Scheiner, originally ranging from 1° Sch. to 20° Sch., where an increment of 19° Sch. corresponded to a hundredfold increase in sensitivity, which meant that an increment of 3° Sch. came close to a doubling of sensitivity.


The system was later extended to cover larger ranges and some of its practical shortcomings were addressed by the Austrian scientist Josef Maria Eder (1855–1944) and Flemish-born botanist Walter Hecht (de) (1896–1960), (who, in 1919/1920, jointly developed their Eder–Hecht neutral wedge sensitometer measuring emulsion speeds in Eder–Hecht grades). Still, it remained difficult for manufactures to reliably determine film speeds, often only by comparing with competing products, so that an increasing number of modified semi-Scheiner-based systems started to spread, which no longer followed Scheiner's original procedures and thereby defeated the idea of comparability.


The DIN system, officially DIN standard 4512 by Deutsches Institut für Normung (but still named Deutscher Normenausschuß (DNA) at this time), was published in January 1934. It grew out of drafts for a standardized method of sensitometry put forward by Deutscher Normenausschuß für Phototechnik as proposed by the committee for sensitometry of the Deutsche Gesellschaft für photographische Forschung since 1930 and presented by Robert Luther (de) (1868–1945) and Emanuel Goldberg (1881–1970) at the influential VIII. International Congress of Photography (German: Internationaler Kongreß für wissenschaftliche und angewandte Photographie) held in Dresden from August 3 to 8, 1931.


As in the Scheiner system, speeds were expressed in 'degrees'. Originally the sensitivity was written as a fraction with 'tenths' (for example "18/10° DIN"), where the resultant value 1.8 represented the relative base 10 logarithm of the speed. 'Tenths' were later abandoned with DIN 4512:1957-11, and the example above would be written as "18° DIN". The degree symbol was finally dropped with DIN 4512:1961-10. This revision also saw significant changes in the definition of film speeds in order to accommodate then-recent changes in the American ASA PH2.5-1960 standard, so that film speeds of black-and-white negative film effectively would become doubled, that is, a film previously marked as "18° DIN" would now be labeled as "21 DIN" without emulsion changes.


On an international level the German DIN 4512 system has been effectively superseded in the 1980s by ISO 6:1974, ISO 2240:1982, and ISO 5800:1979 where the same sensitivity is written in linear and logarithmic form as "ISO 100/21°" (now again with degree symbol). These ISO standards were subsequently adopted by DIN as well. Finally, the latest DIN 4512 revisions were replaced by corresponding ISO standards, DIN 4512-1:1993-05 by DIN ISO 6:1996-02 in September 2000, DIN 4512-4:1985-08 by DIN ISO 2240:1998-06 and DIN 4512-5:1990-11 by DIN ISO 5800:1998-06 both in July 2002.


Before the advent of the ASA system, the system of Weston film speed ratings was introduced by Edward Faraday Weston (1878–1971) and his father Dr. Edward Weston (1850–1936), a British-born electrical engineer, industrialist and founder of the US-based Weston Electrical Instrument Corporation, with the Weston model 617, one of the earliest photo-electric exposure meters, in August 1932. The meter and film rating system were invented by William Nelson Goodwin, Jr., who worked for them and later received a Howard N. Potts Medal for his contributions to engineering.


The Weston Cadet (model 852 introduced in 1949), Direct Reading (model 853 introduced 1954) and Master III (models 737 and S141.3 introduced in 1956) were the first in their line of exposure meters to switch and utilize the meanwhile established ASA scale instead. Other models used the original Weston scale up until ca. 1955. The company continued to publish Weston film ratings after 1955, but while their recommended values often differed slightly from the ASA film speeds found on film boxes, these newer Weston values were based on the ASA system and had to be converted for use with older Weston meters by subtracting 1/3 exposure stop as per Weston's recommendation. Vice versa, "old" Weston film speed ratings could be converted into "new" Westons and the ASA scale by adding the same amount, that is, a film rating of 100 Weston (up to 1955) corresponded with 125 ASA (as per ASA PH2.5-1954 and before). This conversion was not necessary on Weston meters manufactured and Weston film ratings published since 1956 due to their inherent use of the ASA system; however the changes of the ASA PH2.5-1960 revision may be taken into account when comparing with newer ASA or ISO values.


General Electric switched to use the ASA scale in 1946. Meters manufactured since February 1946 were equipped with the ASA scale (labeled "Exposure Index") already. For some of the older meters with scales in "Film Speed" or "Film Value" (e.g. models DW-48, DW-49 as well as early DW-58 and GW-68 variants), replaceable hoods with ASA scales were available from the manufacturer. The company continued to publish recommended film values after that date, however, they were now aligned to the ASA scale.


Based on earlier research work by Loyd Ancile Jones (1884–1954) of Kodak and inspired by the systems of Weston film speed ratings and General Electric film values, the American Standards Association (now named ANSI) defined a new method to determine and specify film speeds of black-and-white negative films in 1943. ASA Z38.2.1-1943 was revised in 1946 and 1947 before the standard grew into ASA PH2.5-1954. Originally, ASA values were frequently referred to as American standard speed numbers or ASA exposure-index numbers. (See also: Exposure Index (EI).)


The ASA standard underwent a major revision in 1960 with ASA PH2.5-1960, when the method to determine film speed was refined and previously applied safety factors against under-exposure were abandoned, effectively doubling the nominal speed of many black-and-white negative films. For example, an Ilford HP3 that had been rated at 200 ASA before 1960 was labeled 400 ASA afterwards without any change to the emulsion. Similar changes were applied to the DIN system with DIN 4512:1961-10 and the BS system with BS 1380:1963 in the following years.


Film speed is found from a plot of optical density vs. log of exposure for the film, known as the D–log H curve or Hurter–Driffield curve. There typically are five regions in the curve: the base + fog, the toe, the linear region, the shoulder, and the overexposed region. For black-and-white negative film, the “speed point” m is the point on the curve where density exceeds the base + fog density by 0.1 when the negative is developed so that a point n where the log of exposure is 1.3 units greater than the exposure at point m has a density 0.8 greater than the density at point m. The exposure Hm, in lux-s, is that for point m when the specified contrast condition is satisfied. The ISO arithmetic speed is determined from:


Film speed is used in the exposure equations to find the appropriate exposure parameters. Four variables are available to the photographer to obtain the desired effect: lighting, film speed, f-number (aperture size), and shutter speed (exposure time). The equation may be expressed as ratios, or, by taking the logarithm (base 2) of both sides, by addition, using the APEX system, in which every increment of 1 is a doubling of exposure; this increment is commonly known as a "stop". The effective f-number is proportional to the ratio between the lens focal length and aperture diameter, the diameter itself being proportional to the square root of the aperture area. Thus, a lens set to f/1.4 allows twice as much light to strike the focal plane as a lens set to f/2. Therefore, each f-number factor of the square root of two (approximately 1.4) is also a stop, so lenses are typically marked in that progression: f/1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32, etc.


Upon exposure, the amount of light energy that reaches the film determines the effect upon the emulsion. If the brightness of the light is multiplied by a factor and the exposure of the film decreased by the same factor by varying the camera's shutter speed and aperture, so that the energy received is the same, the film will be developed to the same density. This rule is called reciprocity. The systems for determining the sensitivity for an emulsion are possible because reciprocity holds. In practice, reciprocity works reasonably well for normal photographic films for the range of exposures between 1/1000 second to 1/2 second. However, this relationship breaks down outside these limits, a phenomenon known as reciprocity failure.


Some high-speed black-and-white films, such as Ilford Delta 3200 and Kodak T-MAX P3200, are marketed with film speeds in excess of their true ISO speed as determined using the ISO testing method. For example, the Ilford product is actually an ISO 1000 film, according to its data sheet. The manufacturers do not indicate that the 3200 number is an ISO rating on their packaging. Kodak and Fuji also marketed E6 films designed for pushing (hence the "P" prefix), such as Ektachrome P800/1600 and Fujichrome P1600, both with a base speed of ISO 400.


For digital photo cameras ("digital still cameras"), an exposure index (EI) rating—commonly called ISO setting—is specified by the manufacturer such that the sRGB image files produced by the camera will have a lightness similar to what would be obtained with film of the same EI rating at the same exposure. The usual design is that the camera's parameters for interpreting the sensor data values into sRGB values are fixed, and a number of different EI choices are accommodated by varying the sensor's signal gain in the analog realm, prior to conversion to digital. Some camera designs provide at least some EI choices by adjusting the sensor's signal gain in the digital realm. A few camera designs also provide EI adjustment through a choice of lightness parameters for the interpretation of sensor data values into sRGB; this variation allows different tradeoffs between the range of highlights that can be captured and the amount of noise introduced into the shadow areas of the photo.


Digital cameras have far surpassed film in terms of sensitivity to light, with ISO equivalent speeds of up to 409,600, a number that is unfathomable in the realm of conventional film photography. Faster processors, as well as advances in software noise reduction techniques allow this type of processing to be executed the moment the photo is captured, allowing photographers to store images that have a higher level of refinement and would have been prohibitively time consuming to process with earlier generations of digital camera hardware.


The ISO standard ISO 12232:2006 gives digital still camera manufacturers a choice of five different techniques for determining the exposure index rating at each sensitivity setting provided by a particular camera model. Three of the techniques in ISO 12232:2006 are carried over from the 1998 version of the standard, while two new techniques allowing for measurement of JPEG output files are introduced from CIPA DC-004. Depending on the technique selected, the exposure index rating can depend on the sensor sensitivity, the sensor noise, and the appearance of the resulting image. The standard specifies the measurement of light sensitivity of the entire digital camera system and not of individual components such as digital sensors, although Kodak has reported using a variation to characterize the sensitivity of two of their sensors in 2001.


The Recommended Exposure Index (REI) technique, new in the 2006 version of the standard, allows the manufacturer to specify a camera model’s EI choices arbitrarily. The choices are based solely on the manufacturer’s opinion of what EI values produce well-exposed sRGB images at the various sensor sensitivity settings. This is the only technique available under the standard for output formats that are not in the sRGB color space. This is also the only technique available under the standard when multi-zone metering (also called pattern metering) is used.


The Standard Output Sensitivity (SOS) technique, also new in the 2006 version of the standard, effectively specifies that the average level in the sRGB image must be 18% gray plus or minus 1/3 stop when the exposure is controlled by an automatic exposure control system calibrated per ISO 2721 and set to the EI with no exposure compensation. Because the output level is measured in the sRGB output from the camera, it is only applicable to sRGB images—typically JPEG—and not to output files in raw image format. It is not applicable when multi-zone metering is used.


The CIPA DC-004 standard requires that Japanese manufacturers of digital still cameras use either the REI or SOS techniques, and DC-008 updates the Exif specification to differentiate between these values. Consequently, the three EI techniques carried over from ISO 12232:1998 are not widely used in recent camera models (approximately 2007 and later). As those earlier techniques did not allow for measurement from images produced with lossy compression, they cannot be used at all on cameras that produce images only in JPEG format.


where  is the maximum possible exposure that does not lead to a clipped or bloomed camera output. Typically, the lower limit of the saturation speed is determined by the sensor itself, but with the gain of the amplifier between the sensor and the analog-to-digital converter, the saturation speed can be increased. The factor 78 is chosen such that exposure settings based on a standard light meter and an 18-percent reflective surface will result in an image with a grey level of 18%/√2 = 12.7% of saturation. The factor √2 indicates that there is half a stop of headroom to deal with specular reflections that would appear brighter than a 100% reflecting white surface.


The noise-based speed is defined as the exposure that will lead to a given signal-to-noise ratio on individual pixels. Two ratios are used, the 40:1 ("excellent image quality") and the 10:1 ("acceptable image quality") ratio. These ratios have been subjectively determined based on a resolution of 70 pixels per cm (178 DPI) when viewed at 25 cm (9.8 inch) distance. The signal-to-noise ratio is defined as the standard deviation of a weighted average of the luminance and color of individual pixels. The noise-based speed is mostly determined by the properties of the sensor and somewhat affected by the noise in the electronic gain and AD converter.


The standard specifies how speed ratings should be reported by the camera. If the noise-based speed (40:1) is higher than the saturation-based speed, the noise-based speed should be reported, rounded downwards to a standard value (e.g. 200, 250, 320, or 400). The rationale is that exposure according to the lower saturation-based speed would not result in a visibly better image. In addition, an exposure latitude can be specified, ranging from the saturation-based speed to the 10:1 noise-based speed. If the noise-based speed (40:1) is lower than the saturation-based speed, or undefined because of high noise, the saturation-based speed is specified, rounded upwards to a standard value, because using the noise-based speed would lead to overexposed images. The camera may also report the SOS-based speed (explicitly as being an SOS speed), rounded to the nearest standard speed rating.


Despite these detailed standard definitions, cameras typically do not clearly indicate whether the user "ISO" setting refers to the noise-based speed, saturation-based speed, or the specified output sensitivity, or even some made-up number for marketing purposes. Because the 1998 version of ISO 12232 did not permit measurement of camera output that had lossy compression, it was not possible to correctly apply any of those measurements to cameras that did not produce sRGB files in an uncompressed format such as TIFF. Following the publication of CIPA DC-004 in 2006, Japanese manufacturers of digital still cameras are required to specify whether a sensitivity rating is REI or SOS.[citation needed]


Mexico City, or the City of Mexico (Spanish: Ciudad de México  audio (help·info) American Spanish: [sjuˈða(ð) ðe ˈméxiko]; abbreviated as "CDMX"), is the capital of Mexico. As an "alpha" global city, Mexico City is one of the most important financial centers in the Americas. It is located in the Valley of Mexico (Valle de México), a large valley in the high plateaus at the center of Mexico, at an altitude of 2,240 metres (7,350 ft). The city consists of sixteen municipalities (previously called boroughs).


The Greater Mexico City has a gross domestic product (GDP) of US$411 billion in 2011, making Mexico City urban agglomeration one of the economically largest metropolitan areas in the world. The city was responsible for generating 15.8% of Mexico's Gross Domestic Product and the metropolitan area accounted for about 22% of total national GDP. As a stand-alone country, in 2013, Mexico City would be the fifth-largest economy in Latin America—five times as large as Costa Rica's and about the same size as Peru's.


Mexico’s capital is both the oldest capital city in the Americas and one of two founded by Amerindians (Native Americans), the other being Quito. The city was originally built on an island of Lake Texcoco by the Aztecs in 1325 as Tenochtitlan, which was almost completely destroyed in the 1521 siege of Tenochtitlan, and subsequently redesigned and rebuilt in accordance with the Spanish urban standards. In 1524, the municipality of Mexico City was established, known as México Tenochtitlán, and as of 1585 it was officially known as Ciudad de México (Mexico City). Mexico City served as the political, administrative and financial center of a major part of the Spanish colonial empire. After independence from Spain was achieved, the Federal District was created in 1824.


After years of demanding greater political autonomy, residents were given the right to directly elect a Head of Government and the representatives of the unicameral Legislative Assembly by popular vote in 1997. Ever since, the left-wing Party of the Democratic Revolution (PRD) has controlled both of them. In recent years, the local government has passed a wave of liberal policies, such as abortion on request, a limited form of euthanasia, no-fault divorce, and same-sex marriage. On January 29, 2016, it ceased to be called the Federal District (Spanish: Distrito Federal or D.F.) and is now in transition to become the country's 32nd federal entity, giving it a level of autonomy comparable to that of a state. Because of a clause in the Mexican Constitution, however, as the seat of the powers of the Union, it can never become a state, lest the capital of the country be relocated elsewhere.


The city grew as the population did, coming up against the lake's waters. As the depth of the lake water fluctuated, Mexico City was subject to periodic flooding. A major labor draft, the desagüe, compelled thousands of Indians over the colonial period to work on infrastructure to prevent flooding. Floods were not only an inconvenience but also a health hazard, since during flood periods human waste polluted the city's streets. By draining the area, the mosquito population dropped as did the frequency of the diseases they spread. However, draining the wetlands also changed the habitat for fish and birds and the areas accessible for Indian cultivation close to the capital.


The concept of nobility flourished in New Spain in a way not seen in other parts of the Americas. Spaniards encountered a society in which the concept of nobility mirrored that of their own. Spaniards respected the indigenous order of nobility and added to it. In the ensuing centuries, possession of a noble title in Mexico did not mean one exercised great political power, for one's power was limited even if the accumulation of wealth was not. The concept of nobility in Mexico was not political but rather a very conservative Spanish social one, based on proving the worthiness of the family. Most of these families proved their worth by making fortunes in New Spain outside of the city itself, then spending the revenues in the capital, building churches, supporting charities and building extravagant palatial homes. The craze to build the most opulent residence possible reached its height in the last half of the 18th century. Many of these palaces can still be seen today, leading to Mexico City's nickname of "The city of palaces" given by Alexander Von Humboldt.


The Grito de Dolores ("Cry of Dolores") also known as El Grito de la Independencia ("Cry of Independence"), uttered from the small town of Dolores near Guanajuato on September 16, 1810, is the event that marks the beginning of the Mexican War of Independence and is the most important national holiday observed in Mexico. The "Grito" was the battle cry of the Mexican War of Independence by Miguel Hidalgo y Costilla, a Roman Catholic priest. Hidalgo and several criollos were involved in a planned revolt against the Spanish colonial government, and the plotters were betrayed. Fearing his arrest, Hidalgo commanded his brother Mauricio as well as Ignacio Allende and Mariano Abasolo to go with a number of other armed men to make the sheriff release the pro-independence inmates there on the night of September 15. They managed to set eighty free. Around 6:00 am September 16, 1810, Hidalgo ordered the church bells to be rung and gathered his congregation. Flanked by Allende and Juan Aldama, he addressed the people in front of his church, encouraging them to revolt. The Battle of Guanajuato, the first major engagement of the insurgency, occurred four days later. Mexico's independence from Spain was effectively declared in the Declaration of Independence of the Mexican Empire on September 27, 1821, after a decade of war. Unrest followed for the next several decades, as different factions fought for control of Mexico.


The Battle for Mexico City was the series of engagements from September 8 to September 15, 1847, in the general vicinity of Mexico City during the Mexican–American War. Included are major actions at the battles of Molino del Rey and Chapultepec, culminating with the fall of Mexico City. The U.S. Army under Winfield Scott scored a major success that ended the war. The American invasion into the Federal District was first resisted during the Battle of Churubusco on August 8 where the Saint Patrick's Battalion, which was composed primarily of Catholic Irish and German immigrants, but also Canadians, English, French, Italians, Poles, Scots, Spaniards, Swiss, and Mexican people, fought for the Mexican cause repelling the American attacks. After defeating the Saint Patrick's Battalion, the Mexican–American War came to a close after the United States deployed combat units deep into Mexico resulting in the capture of Mexico City and Veracruz by the U.S. Army's 1st, 2nd, 3rd and 4th Divisions. The invasion culminated with the storming of Chapultepec Castle in the city itself.


During this battle, on September 13, the 4th Division, under John A. Quitman, spearheaded the attack against Chapultepec and carried the castle. Future Confederate generals George E. Pickett and James Longstreet participated in the attack. Serving in the Mexican defense were the cadets later immortalized as Los Niños Héroes (the "Boy Heroes"). The Mexican forces fell back from Chapultepec and retreated within the city. Attacks on the Belén and San Cosme Gates came afterwards. The treaty of Guadalupe Hidalgo was signed in what is now the far north of the city.


During this era of Porfirian rule, the city underwent an extensive modernization. Many Spanish Colonial style buildings were destroyed, replaced by new much larger Porfirian institutions and many outlying rural zones were transformed into urban or industrialized districts with most having electrical, gas and sewage utilities by 1908. While the initial focus was on developing modern hospitals, schools, factories and massive public works, perhaps the most long-lasting effects of the Porfirian modernization were creation of the Colonia Roma area and the development of Reforma Avenue. Many of Mexico City's major attractions and landmarks were built during this era in this style.


Diaz's plans called for the entire city to eventually be modernized or rebuilt in the Porfirian/French style of the Colonia Roma; but the Mexican Revolution began soon afterward and the plans never came to fruition, with many projects being left half-completed. One of the best examples of this is the Monument to the Mexican Revolution. Originally the monument was to be the main dome of Diaz's new senate hall, but when the revolution erupted only the dome of the senate hall and its supporting pillars were completed, this was subsequently seen as a symbol by many Mexicans that the Porfirian era was over once and for all and as such, it was turned into a monument to victory over Diaz.


Zapatist forces, which were based in neighboring Morelos had strengths in the southern edge of the Federal District, which included Xochimilco, Tlalpan, Tláhuac and Milpa Alta to fight against the regimes of Victoriano Huerta and Venustiano Carranza. After the assassination of Carranza and a short mandate by Adolfo de la Huerta, Álvaro Obregón took power. After willing to be re-elected, he was killed by José de León Toral, a devout Catholic, in a restaurant near La Bombilla Park in San Ángel in 1928. Plutarco Elias Calles replaced Obregón and culminated the Mexican Revolution.


In 1980 half of all the industrial jobs in Mexico were located in Mexico City. Under relentless growth, the Mexico City government could barely keep up with services. Villagers from the countryside who continued to pour into the city to escape poverty only compounded the city's problems. With no housing available, they took over lands surrounding the city, creating huge shantytowns that extended for many miles. This caused serious air pollution in Mexico City and water pollution problems, as well as subsidence due to overextraction of groundwater. Air and water pollution has been contained and improved in several areas due to government programs, the renovation of vehicles and the modernization of public transportation.


On Thursday, September 19, 1985, at 7:19 am local time, Mexico City was struck by an earthquake of magnitude 8.1 on the Richter scale. Although this earthquake was not as deadly or destructive as many similar events in Asia and other parts of Latin America, it proved to be a disaster politically for the one-party government. The government was paralyzed by its own bureaucracy and corruption, forcing ordinary citizens to create and direct their own rescue efforts and to reconstruct much of the housing that was lost as well.


Mexico City is located in the Valley of Mexico, sometimes called the Basin of Mexico. This valley is located in the Trans-Mexican Volcanic Belt in the high plateaus of south-central Mexico. It has a minimum altitude of 2,200 meters (7,200 feet) above sea level and is surrounded by mountains and volcanoes that reach elevations of over 5,000 metres (16,000 feet). This valley has no natural drainage outlet for the waters that flow from the mountainsides, making the city vulnerable to flooding. Drainage was engineered through the use of canals and tunnels starting in the 17th century.


Mexico city primarily rests on what was Lake Texcoco. Seismic activity is frequent here. Lake Texcoco was drained starting from the 17th century. Although none of the lake waters remain, the city rests on the lake bed's heavily saturated clay. This soft base is collapsing due to the over-extraction of groundwater, called groundwater-related subsidence. Since the beginning of the 20th century the city has sunk as much as nine metres (30 feet) in some areas. This sinking is causing problems with runoff and wastewater management, leading to flooding problems, especially during the rainy season. The entire lake bed is now paved over and most of the city's remaining forested areas lie in the southern boroughs of Milpa Alta, Tlalpan and Xochimilco.


The area receives about 820 millimetres (32.3 in) of annual rainfall, which is concentrated from June through September/October with little or no precipitation the remainder of the year. The area has two main seasons. The rainy season runs from June to October when winds bring in tropical moisture from the sea. The dry season runs from November to May, when the air is relatively drier. This dry season subdivides into a cold period and a warm period. The cold period spans from November to February when polar air masses push down from the north and keep the air fairly dry. The warm period extends from March to May when tropical winds again dominate but do not yet carry enough moisture for rain.


Originally much of the valley laid beneath the waters of Lake Texcoco, a system of interconnected salt and freshwater lakes. The Aztecs built dikes to separate the fresh water used to raise crops in chinampas and to prevent recurrent floods. These dikes were destroyed during the siege of Tenochtitlan, and during colonial times the Spanish regularly drained the lake to prevent floods. Only a small section of the original lake remains, located outside the Federal District, in the municipality of Atenco, State of Mexico.


By the 1990s Mexico City had become infamous as one of the world's most polluted cities; however the city has become a model for dramatically lowering pollution levels. By 2014 carbon monoxide pollution had dropped dramatically, while levels of sulfur dioxide and nitrogen dioxide were nearly three times lower than in 1992. The levels of signature pollutants in Mexico City are similar to those of Los Angeles.[citation needed] Despite the cleanup, the metropolitan area is still the most ozone-polluted part of the country, with ozone levels 2.5 times beyond WHO-defined safe limits.


To clean up pollution, the federal and local governments implemented numerous plans including the constant monitoring and reporting of environmental conditions, such as ozone and nitrogen oxides. When the levels of these two pollutants reached critical levels, contingency actions were implemented which included closing factories, changing school hours, and extending the A day without a car program to two days of the week. The government also instituted industrial technology improvements, a strict biannual vehicle emission inspection and the reformulation of gasoline and diesel fuels. The introduction of Metrobús bus rapid transit and the Ecobici bike-sharing were among efforts to encourage alternate, greener forms of transportation.


The Acta Constitutiva de la Federación of January 31, 1824, and the Federal Constitution of October 4, 1824, fixed the political and administrative organization of the United Mexican States after the Mexican War of Independence. In addition, Section XXVIII of Article 50 gave the new Congress the right to choose where the federal government would be located. This location would then be appropriated as federal land, with the federal government acting as the local authority. The two main candidates to become the capital were Mexico City and Querétaro.


Due in large part to the persuasion of representative Servando Teresa de Mier, Mexico City was chosen because it was the center of the country's population and history, even though Querétaro was closer to the center geographically. The choice was official on November 18, 1824, and Congress delineated a surface area of two leagues square (8,800 acres) centered on the Zocalo. This area was then separated from the State of Mexico, forcing that state's government to move from the Palace of the Inquisition (now Museum of Mexican Medicine) in the city to Texcoco. This area did not include the population centers of the towns of Coyoacán, Xochimilco, Mexicaltzingo and Tlalpan, all of which remained as part of the State of Mexico.


In 1854 president Antonio López de Santa Anna enlarged the area of the Federal District almost eightfold from the original 220 to 1,700 km2 (80 to 660 sq mi), annexing the rural and mountainous areas to secure the strategic mountain passes to the south and southwest to protect the city in event of a foreign invasion. (The Mexican–American War had just been fought.) The last changes to the limits of the Federal District were made between 1898 and 1902, reducing the area to the current 1,479 km2 (571 sq mi) by adjusting the southern border with the state of Morelos. By that time, the total number of municipalities within the Federal District was twenty-two.


While the Federal District was ruled by the federal government through an appointed governor, the municipalities within it were autonomous, and this duality of powers created tension between the municipalities and the federal government for more than a century. In 1903, Porfirio Díaz largely reduced the powers of the municipalities within the Federal District. Eventually, in December 1928, the federal government decided to abolish all the municipalities of the Federal District. In place of the municipalities, the Federal District was divided into one "Central Department" and 13 delegaciones (boroughs) administered directly by the government of the Federal District. The Central Department was integrated by the former municipalities of Mexico City, Tacuba, Tacubaya and Mixcoac.


In 1941, the General Anaya borough was merged to the Central Department, which was then renamed "Mexico City" (thus reviving the name, but not the autonomous municipality). From 1941 to 1970, the Federal District comprised twelve delegaciones and Mexico City. In 1970 Mexico City was split into four different delegaciones: Cuauhtémoc, Miguel Hidalgo, Venustiano Carranza and Benito Juárez, increasing the number of delegaciones to sixteen. Since then, in a de facto manner, the whole Federal District, whose delegaciones had by then almost formed a single urban area, began to be considered a synonym of Mexico City.


Mexico City, being the seat of the powers of the Union, did not belong to any particular state but to all. Therefore, it was the president, representing the federation, who used to designate the head of government of the Federal District, a position which is sometimes presented outside Mexico as the "Mayor" of Mexico City.[citation needed] In the 1980s, given the dramatic increase in population of the previous decades, the inherent political inconsistencies of the system, as well as the dissatisfaction with the inadequate response of the federal government after the 1985 earthquake, residents began to request political and administrative autonomy to manage their local affairs.[citation needed] Some political groups even proposed that the Federal District be converted into the 32nd state of the federation.


In response to the demands, in 1987 the Federal District received a greater degree of autonomy, with the elaboration the first Statute of Government (Estatuto de Gobierno), and the creation of an Assembly of Representatives.[citation needed] In the 1990s, this autonomy was further expanded and, starting from 1997, residents can directly elect the head of government of the Federal District and the representatives of a unicameral Legislative Assembly (which succeeded the previous Assembly) by popular vote.


The first elected head of government was Cuauhtémoc Cárdenas. Cárdenas resigned in 1999 to run in the 2000 presidential elections and designated Rosario Robles to succeed him, who became the first woman (elected or otherwise) to govern Mexico City. In 2000 Andrés Manuel López Obrador was elected, and resigned in 2005 to run in the 2006 presidential elections, Alejandro Encinas being designated by the Legislative Assembly to finish the term. In 2006, Marcelo Ebrard was elected for the 2006–2012 period.


The Legislative Assembly of the Federal District is formed, as it is the case in all legislatures in Mexico, by both single-seat and proportional seats, making it a system of parallel voting. The Federal District is divided into 40 electoral constituencies of similar population which elect one representative by first-past-the-post plurality (FPP), locally called "uninominal deputies". The Federal District as a whole constitutes a single constituency for the parallel election of 26 representatives by proportionality (PR) with open-party lists, locally called "plurinominal deputies".


Even though proportionality is confined to the proportional seats to prevent a part from being overrepresented, several restrictions apply in the assignation of the seats; namely, that no party can have more than 63% of all seats, both uninominal and plurinominal. In the 2006 elections leftist PRD got the absolute majority in the direct uninominal elections, securing 34 of the 40 FPP seats. As such, the PRD was not assigned any plurinominal seat to comply with the law that prevents over-representation. The overall composition of the Legislative Assembly is:


The politics pursued by the administrations of heads of government in Mexico City since the second half of the 20th century have usually been more liberal than those of the rest of the country, whether with the support of the federal government—as was the case with the approval of several comprehensive environmental laws in the 1980s—or through laws recently approved by the Legislative Assembly. In April of the same year, the Legislative Assembly expanded provisions on abortions, becoming the first federal entity to expand abortion in Mexico beyond cases of rape and economic reasons, to permit it regardless of the reason should the mother request it before the twelfth week of pregnancy. In December 2009, the Federal District became the first city in Latin America, and one of very few in the world, to legalize same-sex marriage.


For administrative purposes, the Federal District is divided into 16 "delegaciones" or boroughs. While not fully equivalent to a municipality, the 16 boroughs have gained significant autonomy, and since 2000 their heads of government are elected directly by plurality (they were previously appointed by the head of government of the Federal District). Given that Mexico City is organized entirely as a Federal District, most of the city services are provided or organized by the Government of the Federal District and not by the boroughs themselves, while in the constituent states these services would be provided by the municipalities. The 16 boroughs of the Federal District with their 2010 populations are:


The boroughs are composed by hundreds of colonias or neighborhoods, which have no jurisdictional autonomy or representation. The Historic Center is the oldest part of the city (along with some other, formerly separate colonial towns such as Coyoacán and San Ángel), some of the buildings dating back to the 16th century. Other well-known central neighborhoods include Condesa, known for its Art Deco architecture and its restaurant scene; Colonia Roma, a beaux arts neighborhood and artistic and culinary hot-spot, the Zona Rosa, formerly the center of nightlife and restaurants, now reborn as the center of the LGBT and Korean-Mexican communities; and Tepito and La Lagunilla, known for their local working-class foklore and large flea markets. Santa María la Ribera and San Rafael are the latest neighborhoods of magnificent Porfiriato architecture seeing the first signs of gentrification.


West of the Historic Center (Centro Histórico) along Paseo de la Reforma are many of the city's wealthiest neighborhoods such as Polanco, Lomas de Chapultepec, Bosques de las Lomas, Santa Fe, and (in the State of Mexico) Interlomas, which are also the city's most important areas of class A office space, corporate headquarters, skyscrapers and shopping malls. Nevertheless, areas of lower income colonias exist in some cases cheek-by-jowl with rich neighborhoods, particularly in the case of Santa Fe.


The south of the city is home to some other high-income neighborhoods such as Colonia del Valle and Jardines del Pedregal, and the formerly separate colonial towns of Coyoacán, San Ángel, and San Jerónimo. Along Avenida Insurgentes from Paseo de la Reforma, near the center, south past the World Trade Center and UNAM university towards the Periférico ring road, is another important corridor of corporate office space. The far southern boroughs of Xochimilco and Tláhuac have a significant rural population with Milpa Alta being entirely rural.


North of the Historic Center, Azcapotzalco and Gustavo A. Madero have important industrial centers and neighborhoods that range from established middle-class colonias such as Claveria and Lindavista to huge low-income housing areas that share hillsides with adjacent municipalities in the State of Mexico. In recent years much of northern Mexico City's industry has moved to nearby municipalities in the State of Mexico. Northwest of Mexico City itself is Ciudad Satélite, a vast middle to upper-middle-class residential and business area.


The Human Development Index report of 2005  shows that there were three boroughs with a very high Human Development Index, 12 with a high HDI value (9 above .85) and one with a medium HDI value (almost high). Benito Juárez borough had the highest HDI of the country (.9510) followed by Miguel Hidalgo which came up 4th nationally with a HDI of (.9189) and Coyoacán (5th nationally) with a HDI value of (.9169). Cuajimalpa, Cuauhtémoc and Azcapotzalco had very high values; respectively .8994 (15th nationally),.8922 (23rd) and .8915 (25th).


In contrast, the boroughs of Xochimilco (172th), Tláhuac (177th) and Iztapalapa (183th) presented the lowest HDI values of the Federal District with values of .8481, .8473 and .8464 respectively—values still in the global high-HDI range. The only borough that did not present a high HDI was that of rural Milpa Alta which presented a "medium" HDI of .7984, far below all other boroughs (627th nationally while the rest stood in the top 200). Mexico City's HDI for the 2005 report was of .9012 (very high), and its 2010 value of .9225 (very high) or (by newer methodology) .8307, and Mexico's highest.


Mexico City is home to some of the best private hospitals in the country; Hospital Ángeles, Hospital ABC and Médica Sur to name a few. The national public healthcare institution for private-sector employees, IMSS, has its largest facilities in Mexico City—including the National Medical Center and the La Raza Medical Center—and has an annual budget of over 6 billion pesos. The IMSS and other public health institutions, including the ISSSTE (Public Sector Employees' Social Security Institute) and the National Health Ministry (SSA) maintain large specialty facilities in the city. These include the National Institutes of Cardiology, Nutrition, Psychiatry, Oncology, Pediatrics, Rehabilitation, among others.


The World Bank has sponsored a project to curb air pollution through public transport improvements and the Mexican government has started shutting down polluting factories. They have phased out diesel buses and mandated new emission controls on new cars; since 1993 all new cars must be fitted with a catalytic converter, which reduces the emissions released. Trucks must use only liquefied petroleum gas (LPG). Also construction of an underground rail system was begun in 1968 in order to help curb air pollution problems and alleviate traffic congestion. Today it has over 201 km (125 mi) of track and carries over 5 million people every day. Fees are kept low to encourage use of the system and during rush hours the crush is so great, that authorities have reserved a special carriage specifically for women. Due to these initiatives and others, the air quality in Mexico City has begun to improve, with the air becoming cleaner since 1991, when the air quality was declared to be a public health risk for 355 days of the year.[citation needed]


Mexico City is one of the most important economic hubs in Latin America. The city proper (Federal District) produces 15.8% of the country's gross domestic product. According to a study conducted by PwC, Mexico City had a GDP of $390 billion, ranking it as the eighth richest city in the world after the greater metropolitan areas of Tokyo, New York City, Los Angeles, Chicago, Paris, London and Osaka/Kobe (and the richest in the whole of Latin America). Excluding the rest of the Mexican economy, Mexico City alone would rank as the 30th largest economy in the world. Mexico City is the greatest contributor to the country's industrial GDP (15.8%) and also the greatest contributor to the country's GDP in the service sector (25.3%). Due to the limited non-urbanized space at the south—most of which is protected through environmental laws—the contribution of the Federal District in agriculture is the smallest of all federal entities in the country. Mexico City has one of the world's fastest-growing economies and its GDP is set to double by 2020.


The economic reforms of President Carlos Salinas de Gortari had a tremendous effect on the city, as a number of businesses, including banks and airlines, were privatized. He also signed the North American Free Trade Agreement (NAFTA). This led to decentralization and a shift in Mexico City's economic base, from manufacturing to services, as most factories moved away to either the State of Mexico, or more commonly to the northern border. By contrast, corporate office buildings set their base in the city.


Historically, and since pre-Hispanic times, the Valley of Anahuac has been one of the most densely populated areas in Mexico. When the Federal District was created in 1824, the urban area of Mexico City extended approximately to the area of today's Cuauhtémoc borough. At the beginning of the 20th century, the elites began migrating to the south and west and soon the small towns of Mixcoac and San Ángel were incorporated by the growing conurbation. According to the 1921 census, 54.78% of the city's population was considered Mestizo (Indigenous mixed with European), 22.79% considered European, and 18.74% considered Indigenous. This was the last Mexican Census which asked people to self-identify themselves with an heritage other than Amerindian. However, the census had the particularity that, unlike racial/ethnic census in other countries, it was focused in the perception of cultural heritage rather than in a racial perception, leading to a good number of white people to identify with "Mixed heritage" due cultural influence. In 1921, Mexico City had less than one million inhabitants.


Up to the 1990s, the Federal District was the most populous federal entity in Mexico, but since then its population has remained stable at around 8.7 million. The growth of the city has extended beyond the limits of the Federal District to 59 municipalities of the state of Mexico and 1 in the state of Hidalgo. With a population of approximately 19.8 million inhabitants (2008), it is one of the most populous conurbations in the world. Nonetheless, the annual rate of growth of the Metropolitan Area of Mexico City is much lower than that of other large urban agglomerations in Mexico, a phenomenon most likely attributable to the environmental policy of decentralization. The net migration rate of the Federal District from 1995 to 2000 was negative.


On the other hand, Mexico City is also home to large communities of expatriates and immigrants, most notably from the rest of North America (U.S. and Canada), from South America (mainly from Argentina and Colombia, but also from Brazil, Chile, Uruguay and Venezuela), from Central America and the Caribbean (mainly from Cuba, Guatemala, El Salvador, Haiti and Honduras); from Europe (mainly from Spain, Germany and Switzerland, but also from Czech Republic, Hungary, France, Italy, Ireland, the Netherlands, Poland and Romania), from the Middle East (mainly from Egypt, Lebanon and Syria); and recently from Asia-Pacific (mainly from China and South Korea). Historically since the era of New Spain, many Filipinos settled in the city and have become integrated in Mexican society. While no official figures have been reported, population estimates of each of these communities are quite significant.


The Historic center of Mexico City (Centro Histórico) and the "floating gardens" of Xochimilco in the southern borough have been declared World Heritage Sites by UNESCO. Famous landmarks in the Historic Center include the Plaza de la Constitución (Zócalo), the main central square with its epoch-contrasting Spanish-era Metropolitan Cathedral and National Palace, ancient Aztec temple ruins Templo Mayor ("Major Temple") and modern structures, all within a few steps of one another. (The Templo Mayor was discovered in 1978 while workers were digging to place underground electric cables).


The most recognizable icon of Mexico City is the golden Angel of Independence on the wide, elegant avenue Paseo de la Reforma, modeled by the order of the Emperor Maximilian of Mexico after the Champs-Élysées in Paris. This avenue was designed over the Americas' oldest known major roadway in the 19th century to connect the National Palace (seat of government) with the Castle of Chapultepec, the imperial residence. Today, this avenue is an important financial district in which the Mexican Stock Exchange and several corporate headquarters are located. Another important avenue is the Avenida de los Insurgentes, which extends 28.8 km (17.9 mi) and is one of the longest single avenues in the world.


Chapultepec Park houses the Chapultepec Castle, now a museum on a hill that overlooks the park and its numerous museums, monuments and the national zoo and the National Museum of Anthropology (which houses the Aztec Calendar Stone). Another piece of architecture is the Fine Arts Palace, a white marble theatre/museum whose weight is such that it has gradually been sinking into the soft ground below. Its construction began during the presidency of Porfirio Díaz and ended in 1934, after being interrupted by the Mexican Revolution in the 1920s. The Plaza of the Three Cultures in the Tlatelolco neighbourhood, and the shrine and Basilicas of Our Lady of Guadalupe are also important sites. There is a double-decker bus, known as the "Turibus", that circles most of these sites, and has timed audio describing the sites in multiple languages as they are passed.


In addition, the city has about 160 museums—the world's greatest single metropolitan concentration —over 100 art galleries, and some 30 concert halls, all of which maintain a constant cultural activity during the whole year. It has either the third or fourth-highest number of theatres in the world after New York, London and perhaps Toronto. Many areas (e.g. Palacio Nacional and the National Institute of Cardiology) have murals painted by Diego Rivera. He and his wife Frida Kahlo lived in Coyoacán, where several of their homes, studios, and art collections are open to the public. The house where Leon Trotsky was initially granted asylum and finally murdered in 1940 is also in Coyoacán.


Mexico City is served by the Sistema de Transporte Colectivo, a 225.9 km (140 mi) metro system, which is the largest in Latin America. The first portions were opened in 1969 and it has expanded to 12 lines with 195 stations. The metro is one of the busiest in the world transporting approximately 4.5 million people every day, surpassed only by subway lines in Moscow (7.5 million), Tokyo (5.9 million), and New York City (5.1 million). It is heavily subsidized, and has some of the lowest fares in the world, each trip costing 5.00 pesos from 05:00 am to midnight. Several stations display pre-Columbian artifacts and architecture that were discovered during the metro's construction.[citation needed] However, the metro covers less than half of the total urban area. The Metro stations are also differentiated by the use of icons and glyphs which were proposed for people who could not read. The specific icons were developed based on historical (characters, sites, pre-Hispanic motifs), linguistic, symbolic (glyphs) or location references and has being emulated in further transportations alternatives in the City and in other Mexican cities. Mexico City is the only city in the world to use the icon reference and has become a popular culture trademark for the city.


The city's first bus rapid transit line, the Metrobús, began operation in June 2005, along Avenida Insurgentes. Line 2 opened in December 2008, serving Eje 4 Sur, line 3 opened in February 2011, serving Eje 1 Poniente, and line 4 opened in April 2012 connecting the airport with San Lázaro and Buenavista Station at Insurgentes. As the microbuses were removed from its route, it was hoped that the Metrobús could reduce pollution and decrease transit time for passengers. In June 2013, Mexico City's mayor announced two more lines to come: Line 5 serving Eje 3 Oriente and Line 6 serving Eje 5 Norte. As of June 2013, 367 Metrobús buses transported 850,000 passengers daily.


In the late 1970s many arterial roads were redesigned as ejes viales; high-volume one-way roads that cross, in theory, Mexico City proper from side to side. The eje vial network is based on a quasi-Cartesian grid, with the ejes themselves being called Eje 1 Poniente, Eje Central, and Eje 1 Oriente, for example, for the north-south roads, and Eje 2 Sur and Eje 3 Norte, for example, for east-west roads. Ring roads are the Circuito Interior (inner ring), Anillo Periférico; the Circuito Exterior Mexiquense ("State of Mexico outer loop") toll road skirting the northeastern and eastern edges of the metropolitan area, the Chamapa-La Venta toll road skirting the northwestern edge, and the Arco Norte completely bypassing the metropolitan area in an arc from northwest (Atlacomulco) to north (Tula, Hidalgo) to east (Puebla). A second level (where tolls are charged) of the Periférico, colloquially called the segundo piso ("second floor"), was officially opened in 2012, with sections still being completed. The Viaducto Miguel Alemán crosses the city east-west from Observatorio to the airport. In 2013 the Supervía Poniente opened, a toll road linking the new Santa Fe business district with southwestern Mexico City.


There is an environmental program, called Hoy No Circula ("Today Does Not Run", or "One Day without a Car"), whereby vehicles that have not passed emissions testing are restricted from circulating on certain days according to the ending digit of their license plates; this in an attempt to cut down on pollution and traffic congestion. While in 2003, the program still restricted 40% of vehicles in the metropolitan area, with the adoption of stricter emissions standards in 2001 and 2006, in practice, these days most vehicles are exempt from the circulation restrictions as long as they pass regular emissions tests.


Street parking in urban neighborhoods is mostly controlled by the franeleros a.k.a. "viene vienes" (lit. "come on, come on"), who ask drivers for a fee to park, in theory to guard the car, but with the implicit threat that the franelero will damage the car if the fee is not paid. Double parking is common (with franeleros moving the cars as required), impeding on the available lanes for traffic to pass. In order to mitigate that and other problems and to raise revenue, 721 parking meters (as of October 2013), have been installed in the west-central neighborhoods Lomas de Chapultepec, Condesa, Roma, Polanco and Anzures, in operation from 8 AM to 8 PM on weekdays and charging a rate of 2 pesos per 15 minutes, with offenders' cars booted, costing about 500 pesos to remove. 30 percent of the monthly 16 million-peso (as of October 2013) income from the parking-meter system (named "ecoParq") is earmarked for neighborhood improvements. The granting of the license for all zones exclusively to a new company without experience in operating parking meters, Operadora de Estacionamientos Bicentenario, has generated controversy.


The local government continuously strives for a reduction of massive traffic congestion, and has increased incentives for making a bicycle-friendly city. This includes North America's second-largest bicycle sharing system, EcoBici, launched in 2010, in which registered residents can get bicycles for 45 minutes with a pre-paid subscription of 300 pesos a year. There are, as of September 2013, 276 stations with 4,000 bicycles across an area stretching from the Historic center to Polanco. within 300 metres (980 feet) of one another and are fully automatic using a transponder based card. Bicycle-service users have access to several permanent Ciclovías (dedicated bike paths/lanes/streets), including ones along Paseo de la Reforma and Avenida Chapultepec as well as one running 59 kilometres (37 miles) from Polanco to Fierro del Toro, which is located south of Cumbres del Ajusco National Park, near the Morelos state line. The city's initiative is inspired by forward thinking examples, such as Denmark's Copenhagenization.


Mexico City is served by Mexico City International Airport (IATA Airport Code: MEX). This airport is Latin America's second busiest and one of the largests in traffic, with daily flights to United States and Canada, mainland Mexico, Central America and the Caribbean, South America, Europe and Asia. Aeroméxico (Skyteam) is based at this airport, and provide codeshare agreements with non-Mexican airlines that span the entire globe. In 2014, the airport handled well over 34 million passengers, just over 2 million more than the year before. This traffic exceeds the current capacity of the airport, which has historically centralized the majority of air traffic in the country. An alternate option is Lic. Adolfo López Mateos International Airport (IATA Airport Code: TLC) in nearby Toluca, State of Mexico, although due to several airlines' decisions to terminate service to TLC, the airport has seen a passenger drop to just over 700,000 passengers in 2014 from over 2.1 million passengers just four years prior.


In the Mexico City airport, the government engaged in an extensive restructuring program that includes the addition of a new second terminal, which began operations in 2007, and the enlargement of four other airports (at the nearby cities of Toluca, Querétaro, Puebla and Cuernavaca) that, along with Mexico City's airport, comprise the Grupo Aeroportuario del Valle de México, distributing traffic to different regions in Mexico. The city of Pachuca will also provide additional expansion to central Mexico's airport network. Mexico City's airport is the main hub for 11 of the 21 national airline companies.


During his annual state-of-the-nation address on September 2, 2014, President of Mexico Enrique Peña Nieto unveiled plans for a new international airport to ease the city's notorious air traffic congestion, tentatively slated for a 2018 opening. The new airport, which would have six runways, will cost $9.15 billion and would be built on vacant federal land east of Mexico City International Airport. Goals are to eventually handle 120 million passengers a year, which would make it the busiest airport in the world.


Having been capital of a vast pre-Hispanic empire, and also the capital of richest viceroyalty within the Spanish Empire (ruling over a vast territory in the Americas and Spanish West Indies), and, finally, the capital of the United Mexican States, Mexico City has a rich history of artistic expression. Since the mesoamerican pre-Classical period the inhabitants of the settlements around Lake Texcoco produced many works of art and complex craftsmanship, some of which are today displayed at the world-renowned National Museum of Anthropology and the Templo Mayor museum. While many pieces of pottery and stone-engraving have survived, the great majority of the Amerindian iconography was destroyed during the Conquest of Mexico.


Much of the early colonial art stemmed from the codices (Aztec illustrated books), aiming to recover and preserve some Aztec and other Amerindian iconography and history. From then, artistic expressions in Mexico were mostly religious in theme. The Metropolitan Cathedral still displays works by Juan de Rojas, Juan Correa and an oil painting whose authorship has been attributed to Murillo. Secular works of art of this period include the equestrian sculpture of Charles IV of Spain, locally known as El Caballito ("The little horse"). This piece, in bronze, was the work of Manuel Tolsá and it has been placed at the Plaza Tolsá, in front of the Palacio de Minería (Mining Palace). Directly in front of this building is the beautiful Museo Nacional de Arte (Munal) (the National Museum of Art).


During the 19th century, an important producer of art was the Academia de San Carlos (San Carlos Art Academy), founded during colonial times, and which later became the Escuela Nacional de Artes Plásticas (the National School of Arts) including painting, sculpture and graphic design, one of UNAM's art schools. Many of the works produced by the students and faculty of that time are now displayed in the Museo Nacional de San Carlos (National Museum of San Carlos). One of the students, José María Velasco, is considered one of the greatest Mexican landscape painters of the 19th century. Porfirio Díaz's regime sponsored arts, especially those that followed the French school. Popular arts in the form of cartoons and illustrations flourished, e.g. those of José Guadalupe Posada and Manuel Manilla. The permanent collection of the San Carlos Museum also includes paintings by European masters such as Rembrandt, Velázquez, Murillo, and Rubens.


During the 20th century, many artists immigrated to Mexico City from different regions of Mexico, such as Leopoldo Méndez, an engraver from Veracruz, who supported the creation of the socialist Taller de la Gráfica Popular (Popular Graphics Workshop), designed to help blue-collar workers find a venue to express their art. Other painters came from abroad, such as Catalan painter Remedios Varo and other Spanish and Jewish exiles. It was in the second half of the 20th century that the artistic movement began to drift apart from the Revolutionary theme. José Luis Cuevas opted for a modernist style in contrast to the muralist movement associated with social politics.


Mexico City has numerous museums dedicated to art, including Mexican colonial, modern and contemporary art, and international art. The Museo Tamayo was opened in the mid-1980s to house the collection of international contemporary art donated by famed Mexican (born in the state of Oaxaca) painter Rufino Tamayo. The collection includes pieces by Picasso, Klee, Kandinsky, Warhol and many others, though most of the collection is stored while visiting exhibits are shown. The Museo de Arte Moderno (Museum of Modern Art) is a repository of Mexican artists from the 20th century, including Rivera, Orozco, Siqueiros, Kahlo, Gerzso, Carrington, Tamayo, among others, and also regularly hosts temporary exhibits of international modern art. In southern Mexico City, the Museo Carrillo Gil (Carrillo Gil Museum) showcases avant-garde artists, as does the University Museum/Contemporary Art (Museo Universitario Arte Contemporáneo – or MUAC), designed by famed Mexican architect Teodoro González de León, inaugurated in late 2008.


The Museo Soumaya, named after the wife of Mexican magnate Carlos Slim, has the largest private collection of original Rodin sculptures outside Paris. It also has a large collection of Dalí sculptures, and recently began showing pieces in its masters collection including El Greco, Velázquez, Picasso and Canaletto. The museum inaugurated a new futuristic-design facility in 2011 just north of Polanco, while maintaining a smaller facility in Plaza Loreto in southern Mexico City. The Colección Júmex is a contemporary art museum located on the sprawling grounds of the Jumex juice company in the northern industrial suburb of Ecatepec. It is said to have the largest private contemporary art collection in Latin America and hosts pieces from its permanent collection as well as traveling exhibits by leading contemporary artists. The new Museo Júmex in Nuevo Polanco was slated to open in November 2013. The Museo de San Ildefonso, housed in the Antiguo Colegio de San Ildefonso in Mexico City's historic downtown district is a 17th-century colonnaded palace housing an art museum that regularly hosts world-class exhibits of Mexican and international art. Recent exhibits have included those on David LaChapelle, Antony Gormley and Ron Mueck. The National Museum of Art (Museo Nacional de Arte) is also located in a former palace in the historic center. It houses a large collection of pieces by all major Mexican artists of the last 400 years and also hosts visiting exhibits.


Another major addition to the city's museum scene is the Museum of Remembrance and Tolerance (Museo de la Memoria y Tolerancia), inaugurated in early 2011. The brainchild of two young Mexican women as a Holocaust museum, the idea morphed into a unique museum dedicated to showcasing all major historical events of discrimination and genocide. Permanent exhibits include those on the Holocaust and other large-scale atrocities. It also houses temporary exhibits; one on Tibet was inaugurated by the Dalai Lama in September 2011.


Mexico City is home to a number of orchestras offering season programs. These include the Mexico City Philharmonic, which performs at the Sala Ollin Yoliztli; the National Symphony Orchestra, whose home base is the Palacio de Bellas Artes (Palace of the Fine Arts), a masterpiece of art nouveau and art decó styles; the Philharmonic Orchestra of the National Autonomous University of Mexico (OFUNAM), and the Minería Symphony Orchestra, both of which perform at the Sala Nezahualcóyotl, which was the first wrap-around concert hall in the Western Hemisphere when inaugurated in 1976. There are also many smaller ensembles that enrich the city's musical scene, including the Carlos Chávez Youth Symphony, the New World Orchestra (Orquesta del Nuevo Mundo), the National Polytechnical Symphony and the Bellas Artes Chamber Orchestra (Orquesta de Cámara de Bellas Artes).


The city is also a leading center of popular culture and music. There are a multitude of venues hosting Spanish and foreign-language performers. These include the 10,000-seat National Auditorium that regularly schedules the Spanish and English-language pop and rock artists, as well as many of the world's leading performing arts ensembles, the auditorium also broadcasts Grand Opera performances from New York's Metropolitan Opera on giant, high definition screens. In 2007 National Auditorium was selected world's best venue by multiple genre media.


Other popular sites for pop-artist performances include the 3,000-seat Teatro Metropolitan, the 15,000-seat Palacio de los Deportes, and the larger 50,000-seat Foro Sol Stadium, where popular international artists perform on a regular basis. The Cirque du Soleil has held several seasons at the Carpa Santa Fe, in the Santa Fe district in the western part of the city. There are numerous venues for smaller musical ensembles and solo performers. These include the Hard Rock Live, Bataclán, Foro Scotiabank, Lunario, Circo Volador and Voilá Acoustique. Recent additions include the 20,000-seat Arena Ciudad de México, the 3,000-seat Pepsi Center World Trade Center, and the 2,500-seat Auditorio Blackberry.


The Centro Nacional de las Artes (National Center for the Arts has several venues for music, theatre, dance. UNAM's main campus, also in the southern part of the city, is home to the Centro Cultural Universitario (the University Culture Center) (CCU). The CCU also houses the National Library, the interactive Universum, Museo de las Ciencias, the Sala Nezahualcóyotl concert hall, several theatres and cinemas, and the new University Museum of Contemporary Art (MUAC). A branch of the National University's CCU cultural center was inaugurated in 2007 in the facilities of the former Ministry of Foreign Affairs, known as Tlatelolco, in north-central Mexico City.


The Papalote children's museum, which houses the world's largest dome screen, is located in the wooded park of Chapultepec, near the Museo Tecnológico, and La Feria amusement park. The theme park Six Flags México (the largest amusement park in Latin America) is located in the Ajusco neighborhood, in Tlalpan borough, southern Mexico City. During the winter, the main square of the Zócalo is transformed into a gigantic ice skating rink, which is said to be the largest in the world behind that of Moscow's Red Square.


The Cineteca Nacional (the Mexican Film Library), near the Coyoacán suburb, shows a variety of films, and stages many film festivals, including the annual International Showcase, and many smaller ones ranging from Scandinavian and Uruguayan cinema, to Jewish and LGBT-themed films. Cinépolis and Cinemex, the two biggest film business chains, also have several film festivals throughout the year, with both national and international movies. Mexico City tops the world in number of IMAX theatres,[citation needed] providing residents and visitors access to films ranging from documentaries to popular blockbusters on these especially large, dramatic screens.


Mexico City offers a variety of cuisines. Restaurants specializing in the regional cuisines of Mexico's 31 states are available in the city. Also available are an array of international cuisines, including Canadian, French, Italian, Croatian, Spanish (including many regional variations), Jewish, Lebanese, Chinese (again with regional variations), Indian, Japanese, Korean, Thai, Vietnamese; and of course fellow Latin American cuisines such as Argentine, Brazilian, and Peruvian. Haute, fusion, kosher, vegetarian and vegan cuisines are also available, as are restaurants solely based on the concepts of local food and slow Food.


The city also has several branches of renowned international restaurants and chefs. These include Paris' Au Pied de Cochon and Brasserie Lipp, Philippe (by Philippe Chow); Nobu, Morimoto; Pámpano, owned by Mexican-raised opera legend Plácido Domingo. There are branches of the exclusive Japanese restaurant Suntory, Rome's famed Alfredo, as well as New York steakhouses Morton's and The Palm, and Monte Carlo's BeefBar. Three of the most famous Lima-based Haute Peruvian restaurants, La Mar, Segundo Muelle and Astrid y Gastón have locations in Mexico City.