2001 National Land Cover Data (NLCD 2001)
NLCD 1992 was a success, and its success had a lot to do with building the momentum for NLCD 2001. NLCD 2001 improves upon NLCD 1992 in three important ways. Whereas NLCD 1992 was simply a land-cover data set, NLCD 2001 is a land-cover database comprised of three elements: land cover, impervious surface and canopy density. Second, NLCD 2001 used improved classification algorithms (PDF) (11pp, 2MB, About PDF), which have resulted in data with more precise rendering of spatial boundaries between the 16 classes (an additional nine classes are available in coastal areas and another four classes in Alaska only). Third, NLCD 2001 also includes Alaska, Hawaii, and Puerto Rico. NLCD 1992 was restricted to the conterminous United States.
NLCD 2001 land cover (Gainesville, FL): The land cover data distinguishes 16 different classes. The land-cover image shows the heterogeneous mixture of land-cover types, including the intermixing of evergreen (dark green), deciduous (light green), forested wetland (purple) and agriculture (yellow) on which an urban fabric (reds and pink) has been superimposed.
NLCD 2001 impervious surface (Boston Metro Area): The impervious surface data classifies each pixel into 101 possible values (0% - 100%). The data show the detailed urban fabric in which many of us reside. Low percentage impervious is in light gray with increasing values depicted in darker gray and the highest value in pink and red. White areas have no impervious surface.
NLCD 2001 canopy density (southwest Colorado): Like the impervious surface data, the canopy density database element classifies each pixel into 101 possible values (0% - 100%). The canopy density estimate apply to the forest only. These data can be combined with the land cover to estimate canopy density by forest type (deciduous, evergreen, mixed, woody wetland)
Several journal articles have been published describing various aspects of the classification process.
Accuracy assessment of the 2001 NLCD is currently underway.