The North American Landscape Characterization (NALC) project is a component of the Landsat Pathfinder Program, which is part of a larger Pathfinder Program initiated by the National Aeronautics and Space Administration (NASA) in 1989. The NALC project is a cooperative effort between NASA, the U.S. Environmental Protection Agency, and the U.S. Geological Survey to make Landsat data available to the widest possible user community for scientific research and for the general public interest. The objectives of the NALC project are to develop standardized remotely sensed data sets and analysis methods in support of investigations of changes in land cover, to develop inventories of terrestrial carbon stocks, to assess carbon cycling dynamics, and to map terrestrial sources of greenhouse gas (CO, CO2, CH4, and N2) emissions. The NALC data set is comprised of hundreds of triplicates (i.e., multispectral scanner (MSS) data acquired in the years 1973, 1986, and 1991 plus or minus 1 year, thus, the name triplicate). The NALC triplicates also include digital elevation model data. The specific temporal windows vary for geographical regions based on the seasonal characteristics of the vegetation cover. In accordance with the Landsat Pathfinder Program concept, the Pathfinder basic data sets are to be comprised of data which have had systematic radiometric and systematic geometric corrections applied to them. The NALC triplicates, however, are precision corrected for geocoding purposes.