NLCD 2006 quantifies land cover and land cover change between the years 2001 to 2006 and provides an updated version of NLCD 2001. These products represent the first time this type of 30-meter cell land cover change has been produced for the conterminous United States. Products were generated by comparing spectral characteristics of Landsat imagery between 2001 and 2006, on an individual path/row basis, using protocols to identify and label change based on the trajectory from NLCD 2001 products. A formal accuracy assessment of the NLCD 2006 land cover change product is planned for 2011.

Generation of NLCD 2006 products helped to identify some update issues in the NLCD 2001 land cover and percent developed imperviousness products only (there were no changes to the NLCD 2001 percent canopy). These issues were evaluated and corrected, necessitating a reissue of NLCD 2001 products (NLCD 2001 Version 2.0) as part of the NLCD 2006 release. A majority of NLCD 2001 updates occur in coastal mapping zones where NLCD 2001 was published prior to the National Oceanic and Atmospheric Administration (NOAA) Coastal Change Analysis Program (C-CAP) 2001 land cover products. NOAA C-CAP 2001 land cover has now been seamlessly integrated with NLCD 2001 land cover for all coastal zones. NLCD 2001 percent developed imperviousness was also updated as part of this process.

The National Land Cover Database 2001 (NLCD 2001) is the next generation land cover classification for the Nation and the first that will include Hawaii, Alaska, and Puerto Rico. The NLCD 2001 details 21 classes of land cover for the entire United States and Puerto Rico, plus a per-pixel estimate of the imperviousness of the land cover and the percentage of tree canopy. The increased effectiveness of this database comes from using 1,780 Landsat 5 and Landsat 7 images from the spring, summer, and fall growing seasons over a 2-year period as well as ancillary data such as the slope, aspect (exposure), elevation, and topographic position. The process began with the preclassification of similar land cover into 66 mapping zones for the conterminous United States and 13 zones for Alaska. The spatial resolution is 30 meters (roughly 98 feet), so scientists can identify objects slightly larger than a baseball diamond. Land cover affects the very basics needed to sustain life. It is also constantly changing. Land cover affects climate, air quality, water safety, the spread of disease, the ability to control natural disasters such as flooding or wildfires, the variety and health of agriculture and ranching, transportation, and communication technology. Land cover influences community and individual prosperity.

NLCD 92 (National Land Cover Data 1992) is a 21-category land cover classification scheme that has been applied consistently over the conterminous U.S. It is based primarily on the unsupervised classification of Landsat TM (Thematic Mapper) 1992 imagery. Ancillary data sources included topography, census, agricultural statistics, soil characteristics, other land cover maps, and wetlands data. The NLCD 92 classification is provided as raster data with a spatial resolution of 30 meters.

The seamless product consists of NLCD 92 for the conterminous U.S., which is provided according to a user-specified area of coverage. The data is expressed in geographic coordinates (latitude/longitude), and it is referenced to the North American Datum of 1983 (NAD83).