Rapid urbanization and city growth have drawn segments of the rural population inward to urban centers. The global population was split evenly between rural and urban areas for the first time in 2008; by 2050, it is expected that 70% of the global population will be concentrated in urban areas.

These population increases in urban areas may be accompanied by housing deficits and insufficient or overburdened social services. In many places, unplanned and rapid urbanization has resulted in residents residing in marginalized spaces, either in informal settlements or on the street.