Urban populations have skyrocketed globally and today represent more than
half of the world’s population. In some parts of the developing world, this
growth has more-than-proportionately involved rural migration to informal
settlements in and around cities, known more commonly as “slums”— densely
populated urban areas characterized by poor-quality housing, a lack of adequate living
space and public services, and accommodating large numbers of informal residents
with generally insecure tenure.1 Worldwide, at least 860 million people are now living
in slums, and the number of slum dwellers grew by six million each year from 2000
to 2010 (UN-Habitat 2012a).