The National Map
The USGS collects and maintains data that show both natural and manmade land cover of the United States. These data are collected from orbiting Landsat satellites and produced for access through the National Land Cover Database (NLCD) for three epochs: 1992, 2001, and 2006. NLCD 1992 and 2006 encompass the conterminous United States, whereas NLCD 2001 encompasses all 50 States and Puerto Rico. NLCD 1992 is a 21-class land cover classification scheme that includes urban, agricultural, rangeland, forest, surface waters, wetlands, barren lands, tundra, and perennial ice/snow classes. The spatial resolution of the data is 30 meters. NLCD 2001 is a 16-class land cover classification scheme (with an additional four classes in Alaska only) also at a spatial resolution of 30 meters, but improves on NLCD 1992 by offering three different products: land cover, percent developed impervious surface, and percent tree canopy density. NLCD 2006 quantifies land cover change for the conterminous U.S. between the years 2001 to 2006. Generation of NLCD 2006 helped identify and correct issues in the NLCD 2001 land cover and percent developed impervious surface products only, and no changes were made to the NLCD 2001 percent tree canopy product. Further information and data download available at: http://www.mrlc.gov/.