GTOPO30 Description: GTOPO30 a global digital elevation model (DEM) with horizontal grid spacing of 30 arc seconds (approx. 1 kilometer) developed over a three year period
by the U.S. Geological Survey's EROS Data
Center (EDC) and supported by our 3D GIS mapping software Global Mapper. Derived from several raster and vector sources such as Digital terrain Elevation Data, Digital Chart of the World, USGS Digital Elevation Models, International Map of the World and more. For easier electronic distribution, GTOPO30 has been divided into 33 smaller tiles listing latitude and longitude extent, elevation statistics and names for each tile. GTOPO30 data processing produced individual continental and regional areas, developed and refined over the ongoing 3 year project period. Vector cartographic processing consisted of converting elevation grids through a vector-to-raster gridding approach. DEM merging of the generalized raster sources and the gridded vector sources was accomplished by mosaicking the data sets. GTOPO30 files are very large; note file sizes before downloading these to your computer. Detailed characteristics information of GTOPO30 including the accuracy, data sources, data distribution format, production methods, and support for GIS mapping users available on the GTOPO30 website with links provided below. Available for free? Yes. Web Pages and FTP Sites: | 
