What drives the formation of suburban slums?

• Suburban slums in developing countries may be a simple extension of core city slums, driven by the rapid growth of low-income households.
• They may be the product of laxer enforcement regimes of local governments in suburban areas.
• They may reflect lower land prices in suburban areas, creating less inducement for public or private stakeholders to evict them.
• They may reflect past economic geographies, e.g., former industrial communities that have since moved to peri-urban areas.
• They may emerge in areas that were formerly middle class, as is occurring in some western countries today. 
• As energy prices increase, housing in urban nodes will rise in price faster than in suburban areas with limited employment and public transport access, resulting in possible disinvestment.
• Most central city slums are built at high densities – often between 600 and 1,800 people per hectare.
• The highest density slum in the world is Dharavi in Mumbai, home to over one million people (2003) living in an area of 175 hectares.
• Some informal communities feature formal, multistory apartment buildings where land and building ownership is clearly established. 
• In China, low-quality housing is frequently mid-rise, 6-8 story buildings built during the 1960s. 
• In some developing (and developed) country cities, housing built for the poor, either by the public sector (sometimes ironically to replace conventional slum housing) or by private developers, has deteriorated into slum conditions.
• Slums in the established, built-up areas of metropolitan systems mainly encroach on public lands (owned by government agencies, state enterprises, etc.). 
• State lands are often easy targets because of weak enforcement of land rights by public authorities and/or political motives, e.g., populist politicians may want to garner support from the poor. 
• In other cases, politicians may fear protests and violence related to lack of housing for the poor, particularly in-migrants.
• Another major location of slum communities in developing country cities are natural areas (officially protected or not), such as river banks, wetlands, steep slope land and public parks (e.g., in Dhaka). 
• Encroachment of slums on natural areas may increase environmental risks for themselves and for the city as a whole, by reducing land for environmental services. 
• As indicated above, slum dwellers generally try to locate on available land (i.e., where they will not be immediately evicted) that is most accessible to livelihood opportunities.