suffer upgrading schemes or when they are resettled to formal housing. for example, it was recently proved that in a small favela in the northeast of brazil (favela sururu de capote), the migration of dismissed sugar cane factory workers to the city of maceió (who initiated the self-construction of the favela), has been driven by the necessity to find a job in the city. the same observation was noticed on the new migrants who contribute to the consolidation and growth of the slum. also, the choice of the terrain for the construction of the favela (the margins of a lagoon) followed the rationale that it could offer conditions to provide them means of work. circa 80% of residents living in that community live from the fishery of a mussel which divides the community through gender and age. alleys and houses were planned to facilitate the working activities, that provided subsistence and livelihood to the community. when resettled, the main reason of changes of formal housing units was due to the lack of possibilities to perform their work in the new houses designed according to formal architecture principles, or even by the distances they had to travel to work in the slum where they originally lived, which was in turn faced by residents by self-constructing spaces to shelter the work originally performed in the slum, in the formal housing units. similar observations were made in other slums. residents also reported that their work constitutes their dignity, citizenship, and self-esteem in the underprivileged settings in which they live. the reflection of this recent research was possible due to participatory observations and the fact that the author of the research has lived in a slum to verify the socioeconomic practices which were prone to shape, plan and govern space in slums. poverty urban poverty encourages the formation and demand for slums. with rapid shift from rural to urban life, poverty migrates to urban areas. the urban poor arrives with hope, and very little of anything else. they typically have no access to shelter, basic urban services and social amenities. slums are often the only option for the urban poor. a woman from a slum is taking a bath in a river. politics many local and national governments have, for political interests, subverted efforts to remove, reduce or upgrade slums into better housing options for the poor. throughout the second half of the 19th century, for example, french political parties relied on votes from slum population and had vested interests in maintaining that voting block. removal and replacement of slum created a conflict of interest, and politics prevented efforts to remove, relocate or upgrade the slums into housing projects that are better than the slums. similar dynamics are cited in favelas of brazil, slums of india, and shanty towns of kenya. the location of 100 largest "contiguous" mega-slums in the world. numerous other regions have slums, but those slums are scattered. the numbers show population in millions per mega-slum, the initials are derived from city name. some of the largest slums of the world are in areas of political or social conflicts. scholars claim politics also drives rural-urban migration and subsequent settlement patterns. pre-existing patronage networks, sometimes in the form of gangs and other times in the form of political parties or social activists, inside slums seek to maintain their economic, social and political power. these social and political groups have vested interests to encourage migration by ethnic groups that will help maintain the slums, and reject alternate housing options even if the alternate options are better in every aspect than the slums they seek to replace. social conflicts millions of lebanese people formed slums during the lebanese civil war from 1975 to 1990. similarly, in recent years, numerous slums have sprung around kabul to accommodate rural afghans escaping taliban violence. natural disasters major natural disasters in poor nations often lead to migration of disaster-affected families from areas crippled by the disaster to unaffected areas, the creation of temporary tent city and slums, or expansion of existing slums. these slums tend to become permanent because the residents do not want to leave, as in the case of slums near port-au-prince after the 2010 haiti earthquake, and slums near dhaka after 2007 bangladesh cyclone sidr. slums in developing countries slum in tai hang, hong kong, in the 1990s location and growth slums typically begin at the outskirts of a city. over time, the city may expand past the original slums, enclosing the slums inside the urban perimeter. new slums sprout at the new boundaries of the expanding city, usually on publicly owned lands, thereby creating an urban sprawl mix of formal settlements, industry, retail zones and slums. this makes the original slums valuable property, densely populated with many conveniences attractive to the poor. at their start, slums are typically located in least desirable lands near the town or city, that are state owned or philanthropic trust owned or religious entity owned or have no clear land title. in cities located over a mountainous terrain, slums begin on difficult to reach slopes 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. initial homes tend to be tents and shacks that are quick to install, but as slum grows, becomes established and newcomers pay the informal association or gang for the right to live in the slum, the construction materials for the slums switches to more lasting materials such as bricks and concrete, suitable for slum's topography. the original slums, over time, get established next to centers of economic activity, schools, hospitals, sources of employment, which the poor rely on. established old slums, surrounded by the formal city infrastructure, cannot expand horizontally; therefore, they grow vertically by stacking additional rooms, sometimes for a growing family and sometimes as a source of rent from new arrivals in slums. some slums name themselves after founders of political parties, locally respected historical figures, current politicians or politician's spouse to garner political backing against eviction. insecure tenure informality of land tenure is a key characteristic of urban slums. at their start, slums are typically located in least desirable lands near the town or city, that are state owned or philanthropic trust owned or religious entity owned or have no clear land title. some immigrants regard unoccupied land as land without owners and therefore occupy it. in some cases the local community or the government allots lands to people, which will later develop into slums and over which the dwellers don't have property rights. informal land tenure also includes occupation of land belonging to someone else. according to flood, 51 percent of slums are based on invasion to private land in sub-saharan africa, 39 percent in north africa and west asia, 10 percent in south asia, 40 percent in east asia, and 40 percent in latin america and the caribbean. in some cases, once the slum has many residents, the early residents form a social group, an informal association or a gang that controls newcomers, charges a fee for the right to live in the slums, and dictates where and how new homes get built within the slum. the newcomers, having paid for the right, feel they have commercial right to the home in that slum. the slum dwellings, built earlier or in later period as the slum grows, are constructed without checking land ownership rights or building codes, are not registered with the city, and often not recognized by the city or state governments. secure land tenure is important for slum dwellers as an authentic recognition of their residential status in urban areas. it also encourages them to upgrade their housing facilities, which will give them protection against natural and unnatural hazards. undocumented ownership with no legal title to the land also prevents slum settlers from applying for mortgage, which might worsen their financial situations. in addition, without registration of the land ownership, the government has difficulty in upgrading basic facilities and improving the living environment. insecure tenure of the slum, as well as lack of socially and politically acceptable alternatives to slums, also creates difficulty in citywide infrastructure development such as rapid mass transit, electrical line and sewer pipe layout, highways and roads. substandard housing and overcrowding substandard housing in a slum in jakarta, indonesia in the 2000s. slum areas are characterized by substandard housing structures. shanty homes are often built hurriedly, on ad hoc basis, with materials unsuitable for housing. often the construction quality is inadequate to withstand heavy rains, high winds, or other local climate and location. paper, plastic, earthen floors, mud-and-wattle walls, wood held together by ropes, straw or torn metal pieces as roofs are some of the materials of construction. in some cases, brick and cement is used, but without attention to proper design and structural engineering requirements. various space, dwelling placement bylaws and local building codes may also be extensively violated. overcrowding is another characteristic of slums. many dwellings are single room units, with high occupancy rates. each dwelling may be cohabited by multiple families. five and more persons may share a one-room unit; the room is used for cooking, sleeping and living. overcrowding is also seen near sources of drinking water, cleaning, and sanitation where one toilet may serve dozens of families. in a slum of kolkata, india, over 10 people sometimes share a 45 m2 room. in kibera slum of nairobi, kenya, population density is estimated at 2,000 people per hectare — or about 500,000 people in one square mile. however, the density and neighbourhood effects of slum populations may also offer an opportunity to target health interventions. inadequate or no infrastructure slum with tiled roofs and railway, jakarta railway slum resettlement 1975, indonesia. one of the identifying characteristics of slums is the lack of or inadequate public infrastructure. from safe drinking water to electricity, from basic health care to police services, from affordable public transport to fire/ambulance services, from sanitation sewer to paved roads, new slums usually lack all of these. established, old slums sometimes garner official support and get some of these infrastructure such as paved roads and unreliable electricity or water supply. slums usually lack street addresses, which creates further problems. slums often have very narrow alleys that do not allow vehicles (including emergency vehicles) to pass. the lack of services such as routine garbage collection allows rubbish to accumulate in huge quantities. the lack of infrastructure is caused by the informal nature of settlement and no planning for the poor by government officials. fires are often a serious problem. in many countries, local and national government often refuse to recognize slums, because the slum are on disputed land, or because of the fear that quick official recognition will encourage more slum formation and seizure of land illegally. recognizing and notifying slums often triggers a creation of property rights, and requires that the government provide public services and infrastructure to the slum residents. with poverty and informal economy, slums do not generate tax revenues for the government and therefore tend to get minimal or slow attention. in other cases, the narrow and haphazard layout of slum streets, houses and substandard shacks, along with persistent threat of crime and violence against infrastructure workers, makes it difficult to layout reliable, safe, cost effective and efficient infrastructure. in yet others, the demand far exceeds the government bureaucracy's ability to deliver. low socioeconomic status of its residents is another common characteristic attributed to slum residents. problems vulnerability to natural and man-made hazards slums in the city of chau doc, vietnam over river hậu (mekong branch). these slums are on stilts to withstand routine floods which last 3 to 4 months every year. slums are often placed among the places vulnerable to natural disasters such as landslides and floods. in cities located over mountainous terrain, slums begin on slopes difficult