The VEMAP data set includes three georeferencing and three cell area variables. On the CD-ROM and HTTP site, these data files are located under the subdirectory /geog. Note that the area variables are related: varea = (areap/100) * area.
Elevation [m]: Elevation was aggregated from 10-minute Navy Fleet Numeric Oceanographic Center (NFNOC 1985) data (C. Vorosmarty, personal communication). Aggregated elevation for each 0.5 degree cell was computed as a simple mean of nine 10-minute grid cell modal values. Elevations for inland water bodies are included; non- background cell count = 3385.
Latitude [degrees and decimal degrees]: Latitude of grid cell center. Positive for North latitudes. All cells are filled with latitude values; there are no background cells.
Longitude [degrees and decimal degrees]: Longitude of cell center. Scaling factor gives negative degrees for West longitudes. All cells are filled with longitude values; there are no background cells.
Area [km2]: Absolute area of a grid cell. Determined by coordinate geometry.
Percent Land Area [%]: Percent of the area of a 0.5 degree latitude/longitude grid cell that is covered by land and within the VEMAP domain (the conterminous U.S.). Derived from the Kern U.S. EPA 10-km gridded soil coverage, this is the number of non- zero 10-km pixels relative to the total number of pixels in a 0.5 degree cell.
Absolute Land Area [km2]: Absolute area of a grid cell that is covered by land and within the VEMAP domain (the conterminous U.S.). Absolute land area is determined as:
varea = (area) * (areap/100)
A complete user's guide to the VEMAP Phase 1 database, which includes more information about this data set, can be found at http://daac.ornl.gov/daacdata/vemap-1/comp/Phase_1_User_Guide.pdf
The ORNL DAAC maintains additional information associated with the VEMAP Project.
Cite this data set as follows (data citation revised on December 18, 2002):
Kittel, T. G. F., N. A. Rosenbloom, T. H. Painter, D. S. Schimel, H. H. Fisher, A. Grimsdell, VEMAP Participants, C. Daly, and E. R. Hunt, Jr. 1998. VEMAP 1: Georeferencing. ORNL DAAC, Oak Ridge, Tennessee, USA. http://dx.doi.org/10.3334/ORNLDAAC/222
Kittel, T. G. F., N. A. Rosenbloom, T. H. Painter, D. S. Schimel, and VEMAP Modeling Participants. 1995. The VEMAP integrated database for modeling United States ecosystem/vegetation sensitivity to climate change. Journal of Biogeography 22:857-862.