As of 2010, the world contained 4,245 cities with 100,000 or more people. To better understand them, the Monitoring Urban Expansion initiative tracks a stratified global sample of 200 of these cities—collecting and analyzing evidence on the quantity of land required for urban expansion, on its physical organization and affordability, and on the forces affecting it. The initiative is a partnership involving the United Nations Human Settlements Programme (UN Habitat) and the Lincoln Institute of Land Policy.
Monitoring Urban Expansion consists of a four phases of mission-driven research.
Phase I focuses on the mapping and measurement of global urban expansion in the sample of cities from 1990 - 2014, using Landsat satellite imagery.
Phase II focuses on the mapping and measurement of urban layouts in the sample, using high-resolution satellite imagery.
Phase III involves a land and housing survey that focuses on regulatory regimes and on land and housing affordability.
Phase IV will involve the mapping and estimation of urban extent in the entire universe of cities out to 2045.