,

,

,

,

,

,

Georeferenced raster image dataset representing City of Somerville, Massachusetts, impervious surface areas.

This is one of the planimetric coverages developed as part of the aerial survey project of 1996 and updated using new aerial photography collected between 25 March 2004 and 23 April 2004.

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.