to reach or start at the bottom of flood-prone valleys, often hidden from plain view of city center but close to some natural water source. in cities located near lagoons, marshlands and rivers, they start at banks or on stilts above water or the dry river bed; in flat terrain, slums begin on lands unsuitable for agriculture, near city trash dumps, next to railway tracks, and other shunned, undesirable locations. these strategies shield slums from the risk of being noticed and removed when they are small and most vulnerable to local government officials. however, the ad hoc construction, lack of quality control on building materials used, poor maintenance, and uncoordinated spatial design make them prone to extensive damage during earthquakes as well from decay. these risks will be intensified by climate change. a slum in haiti damaged by 2010 earthquake. slums are vulnerable to extensive damage and human fatalities from landslides, floods, earthquakes, fire, high winds and other severe weather. some slums risk man-made hazards such as toxic industries, traffic congestion and collapsing infrastructure. fires are another major risk to slums and its inhabitants, with streets too narrow to allow proper and quick access to fire control trucks. unemployment and informal economy due to lack of skills and education as well as competitive job markets, many slum dwellers face high rates of unemployment. the limit of job opportunities causes many of them to employ themselves in the informal economy, inside the slum or in developed urban areas near the slum. this can sometimes be licit informal economy or illicit informal economy without working contract or any social security. some of them are seeking jobs at the same time and some of those will eventually find jobs in formal economies after gaining some professional skills in informal sectors. examples of licit informal economy include street vending, household enterprises, product assembly and packaging, making garlands and embroideries, domestic work, shoe polishing or repair, driving tuk-tuk or manual rickshaws, construction workers or manually driven logistics, and handicrafts production. in some slums, people sort and recycle trash of different kinds (from household garbage to electronics) for a living – selling either the odd usable goods or stripping broken goods for parts or raw materials. typically these licit informal economies require the poor to regularly pay a bribe to local police and government officials. a propaganda poster linking slum to violence, used by us housing authority in the 1940s. city governments in the usa created many such propaganda posters and launched a media campaign to gain citizen support for slum clearance and planned public housing. examples of illicit informal economy include illegal substance and weapons trafficking, drug or moonshine/changaa production, prostitution and gambling – all sources of risks to the individual, families and society. recent reports reflecting illicit informal economies include drug trade and distribution in brazil's favelas, production of fake goods in the colonías of tijuana, smuggling in katchi abadis and slums of karachi, or production of synthetic drugs in the townships of johannesburg. the slum-dwellers in informal economies run many risks. the informal sector, by its very nature, means income insecurity and lack of social mobility. there is also absence of legal contracts, protection of labour rights, regulations and bargaining power in informal employments. violence from the 1950s to the 1970s, the kowloon walled city in hong kong was controlled by local triads. some scholars suggest that crime is one of the main concerns in slums. empirical data suggest crime rates are higher in some slums than in non-slums, with slum homicides alone reducing life expectancy of a resident in a brazil slum by 7 years than for a resident in nearby non-slum. in some countries like venezuela, officials have sent in the military to control slum criminal violence involved with drugs and weapons. rape is another serious issue related to crime in slums. in nairobi slums, for example, one fourth of all teenage girls are raped each year. on the other hand, while un-habitat reports some slums are more exposed to crimes with higher crime rates (for instance, the traditional inner-city slums), crime is not the direct resultant of block layout in many slums. rather crime is one of the symptoms of slum dwelling; thus slums consist of more victims than criminals. consequently, slums in all do not have consistently high crime rates; slums have the worst crime rates in sectors maintaining influence of illicit economy – such as drug trafficking, brewing, prostitution and gambling –. often in such circumstance, multiple gangs fight for control over revenue. slum crime rate correlates with insufficient law enforcement and inadequate public policing. in main cities of developing countries, law enforcement lags behind urban growth and slum expansion. often police can not reduce crime because, due to ineffective city planning and governance, slums set inefficient crime prevention system. such problems is not primarily due to community indifference. leads and information intelligence from slums are rare, streets are narrow and a potential death traps to patrol, and many in the slum community have an inherent distrust of authorities from fear ranging from eviction to collection on unpaid utility bills to general law and order. lack of formal recognition by the governments also leads to few formal policing and public justice institutions in slums. women in slums are at greater risk of physical and sexual violence. factors such as unemployment that lead to insufficient resources in the household can increase marital stress and therefore exacerbate domestic violence. slums are often non-secured areas and women often risk sexual violence when they walk alone in slums late at night. violence against women and women's security in slums emerge as recurrent issues. another prevalent form of violence in slums is armed violence (gun violence), mostly existing in african and latin american slums. it leads to homicide and the emergence of criminal gangs. typical victims are male slum residents. violence often leads to retaliatory and vigilante violence within the slum. gang and drug wars are endemic in some slums, predominantly between male residents of slums. the police sometimes participate in gender-based violence against men as well by picking up some men, beating them and putting them in jail. domestic violence against men also exists in slums, including verbal abuses and even physical violence from households. cohen as well as merton theorized that the cycle of slum violence does not mean slums are inevitably criminogenic, rather in some cases it is frustration against life in slum, and a consequence of denial of opportunity to slum residents to leave the slum. further, crime rates are not uniformly high in world's slums; the highest crime rates in slums are seen where illicit economy – such as drug trafficking, brewing, prostitution and gambling – is strong and multiple gangs are fighting for control. a young boy sits over an open sewer in the kibera slum, nairobi. infectious diseases and epidemics slum dwellers usually experience a high rate of disease. diseases that have been reported in slums include cholera, hiv/aids, measles, malaria, dengue, typhoid, drug resistant tuberculosis, and other epidemics. studies focus on children's health in slums address that cholera and diarrhea are especially common among young children. besides children's vulnerability to diseases, many scholars also focus on high hiv/aids prevalence in slums among women. throughout slum areas in various parts of the world, infectious diseases are a significant contributor to high mortality rates. for example, according to a study in nairobi's slums, hiv/aids and tuberculosis attributed to about 50% of the mortality burden. factors that have been attributed to a higher rate of disease transmission in slums include high population densities, poor living conditions, low vaccination rates, insufficient health-related data and inadequate health service. overcrowding leads to faster and wider spread of diseases due to the limited space in slum housing. poor living conditions also make slum dwellers more vulnerable to certain diseases. poor water quality, a manifest example, is a cause of many major illnesses including malaria, diarrhea and trachoma. improving living conditions such as introduction of better sanitation and access to basic facilities can ameliorate the effects of diseases, such as cholera. slums have been historically linked to epidemics, and this trend has continued in modern times. for example, the slums of west african nations such as liberia were crippled by as well as contributed to the outbreak and spread of ebola in 2014. slums are considered a major public health concern and potential breeding grounds of drug resistant diseases for the entire city, the nation, as well as the global community. child malnutrition child malnutrition is more common in slums than in non-slum areas. in mumbai and new delhi, 47% and 51% of slum children under the age of five are stunted and 35% and 36% of them are underweighted. these children all suffer from third-degree malnutrition, the most severe level, according to who standards. a study conducted by tada et al. in bangkok slums illustrates that in terms of weight-forage, 25.4% of the children who participated in the survey suffered from malnutrition, compared to around 8% national malnutrition prevalence in thailand. in ethiopia and the niger, rates of child malnutrition in urban slums are around 40%. the major nutritional problems in slums are protein-energy malnutrition (pem), vitamin a deficiency (vad), iron deficiency anemia (ida) and iodine deficiency disorders (idd). malnutrition can sometimes lead to death among children. dr. abhay bang's report shows that malnutrition kills 56,000 children annually in urban slums in india. widespread child malnutrition in slums is closely related to family income, mothers' food practice, mothers' educational level, and maternal employment or housewifery. poverty may result in inadequate food intake when people cannot afford to buy and store enough food, which leads to malnutrition. another common cause is mothers' faulty feeding practices, including inadequate breastfeeding and wrongly preparation of food for children. tada et al.'s study in bangkok slums shows that around 64% of the mothers sometimes fed their children instant food instead of a normal meal. and about 70% of the mothers did not provide their children three meals every day. mothers' lack of education leads to their faulty feeding practices. many mothers in slums don't have knowledge on food nutrition for children. maternal employment also influences children's nutritional status. for the mothers who work outside, their children are prone to be malnourished. these children are likely to be neglected by their mothers or sometimes not carefully looked after by their female relatives. other non-communicable diseases a multitude of non-contagious diseases also impact health for slum residents. examples of prevalent non-infectious diseases include: cardiovascular disease, diabetes, chronic respiratory disease, neurological disorders, and mental illness. in some slum areas of india, diarrhea is a significant health problem among children. factors like poor sanitation, low literacy rates, and limited awareness make diarrhea and other dangerous diseases extremely prevalent and burdensome on the community. lack of reliable data also has a negative impact on slum dwellers' health. a number of slum families do not report cases or seek professional medical care, which results in insufficient data. this might prevent appropriate allocation of health care resources in slum areas since many countries base their health care plans on data from clinic, hospital, or national mortality registry. moreover, health service is insufficient or inadequate in most of the world's slums. emergency ambulance service and urgent care services are typically unavailable, as health service providers sometimes avoid servicing slums. a study shows that more than half of slum dwellers are prone to visit private practitioners or seek self-medication with medicines available in the home. private practitioners in slums are usually those who are unlicensed or poorly trained and they run clinics and pharmacies mainly for the sake of money. the categorization of slum health by the government and census data also has an effect on the distribution and allocation of health resources in inner city areas. a significant portion of city populations face challenges with access to health care but do not live in locations that are described as within the "slum" area. overall, a complex network of physical, social, and environmental factors contribute to the health threats faced by slum residents. countermeasures villa 31, one of the largest slums of argentina, located near the center of buenos aires recent years have seen a dramatic growth in the number of slums as urban