Land-cover and land-use conditions and their changes can affect social and physical environments by altering ecosystem conditions and services. This chapter aims to briefly summarize the methods used and experiences learned from the activities of national land cover database (NLCD) development. In addition to Landsat 5 imagery, other ancillary geospatial data were compiled to support land-cover mapping, including US Geological Survey (USGS) Digital Terrain Elevation Data and its derivatives, US Census Bureau population density data, USGS land use data analysis of 1970s, the National Wetlands Inventory data, and the USDA State Soil Geographic Database. A prototype method was developed by the USGS for updating NLCD 2006. To simplify the class legend during threshold calculations, the NLCD 2001 product was recategorized to eight land-cover classes according to the Anderson level I classification. The land cover is classification using similar procedures as the NLCD 2001 land-cover classification.