GTOPO30 global topographic data. United States Geological Survey (USGS) standard. Distribution format for a global digital elevation model (DEM) with 30-arc-second grid spacing. Binary format. Typically distributed as a compressed archive of multiple files. Uses a horizontal grid spacing of 30 arc seconds (1/120 degrees) or approximately 1 kilometer. Developed 1993-1996 by the USGS Center for Earth Resources Observation and Science.