A Digital Elevation Model (DEM) consists of a sampled array ofelevations for ground positions that are normally at regularly spaced intervals. The Digital Chart of the World (DCW) DEM data provide 30-by-30 arc-second digital elevation data produced from the Defense Mapping Agency's (DMA) 1:1,000,000-scale DCW contour and hydrology data. The EROS Data Center's DCW DEM project includes generation of 30 arc-second data for the entire world to be distributed on CD-ROM as major geographic regions are completed. As of May 1997, 30" DEM Grids for the whole are complete and available for distribution from the website given below.