Booming urban populations have seen poverty on the rise in some of the world's biggest cities. Of the 3.49 billion people that now live in cities, 827.6 million are slum dwellers, according to a UN Habitat Report.

Global slums can be vastly different in nature. Some are working-class neighborhoods that have been torn up by gang wars like the Petare slum in Venezuela. Others like Dharavi in Mumbai, a mini-city that operates as a recycling hub and has a booming leather industry, are a permanent fixture.

Slums like Kibera are notoriously difficult to measure because they often serve as a conduit for people shifting from the country to big cities. This list is not exhaustive and the ones that made our list did so on the basis of their crime rate, size, and population.