Changes in imperviousness for U.S. urban areas, 1974-2012

This product consists of two sets of imperviousness calculations for 3,535 urban areas and urban clusters in the conterminous United States. Imperviousness is given as the percent of the area covered by impervious surfaces, such as roads, buildings, or parking lots. One set of calculations is for the time periods 2001, 2006, and 2011, based on the U.S. Geological Survey (USGS) National Land Cover Dataset (NLCD) imperviousness data layer. The second set of calculations is for the time periods 1974, 1982, 1992, 2002, and 2012, based on landuse-based coefficients from the USGS NAWQA Wall-to-wall Anthropogenic Landuse Trends (NWALT) product. Urban area boundaries are based on the U.S. Census Bureau 2015 Urban Areas boundaries. The Census Bureau polygon shapefile on which the calculations were based is also provided.