A new map of global urban extent from MODIS satellite data

Abstract

Although only a small percentage of global land cover, urban areas significantly alterclimate, biogeochemistry, and hydrology at local, regional, and global scales. To understandthe impact of urban areas on these processes, high quality, regularly updatedinformation on the urban environment—including maps that monitor locationand extent—is essential. Here we present results from efforts to map the globaldistribution of urban land use at 500 m spatial resolution using remotely senseddata from the Moderate Resolution Imaging Spectroradiometer (MODIS). Ourapproach uses a supervised decision tree classification algorithm that we process usingregion-specific parameters. An accuracy assessment based on sites from a stratified randomsample of 140 cities shows that the new map has an overall accuracy of 93% (k = 0.65) at the pixel level and a high level of agreement at the city scale (R2 = 0.90). Our results (available at http://sage.wisc.edu/urbanenvironment.html) also reveal thatthe land footprint of cities occupies less than 0.5% of the Earth’s total land area.