NLCD 2001 Version 2

National Land Cover Database 2001 (NLCD2001) is a 16-class (additional four classes in Alaska only) land cover classification scheme that has been applied consistently across all 50 United States and Puerto Rico at a spatial resolution of 30 meters. NLCD2001 is based primarily on the unsupervised classification of Landsat Enhanced Thematic Mapper+ (ETM+) circa 2001 satellite data. NLCD2001 improves on NLCD92 in that it is comprised of three different elements: land cover, percent developed impervious surface and percent tree canopy density. NLCD2001 also uses improved classification algorithms, which have resulted in data with more precise rending of spatial boundaries between the land cover classes.