Chapter 4. General Characteristics of GLOBE
The Global Land One-Kilometer Base Elevation (GLOBE) digital elevation model (DEM) is a global data set covering 180o West to 180o East longitude and 90o North to 90o South latitude. The horizontal grid spacing is 30 arc-seconds (0.008333... degrees) in latitude and longitude, resulting in dimensions of 21,600 rows and 43,200 columns. At the Equator, a degree of latitude is about 111 kilometers. GLOBE has 120 values per degree, giving GLOBE slightly better than 1 km gridding at the Equator, and progressively finer longitudinally toward the Poles (see Section 6.A).
The horizontal coordinate system is seconds of latitude and longitude referenced to World Geodetic System 84 (WGS84). The vertical units represent elevation in meters above Mean Sea Level. The elevation values range from -407 to 8,752 meters on land. In GLOBE Version 1.0, ocean areas have been masked as "no data" and have been assigned a value of -500.
Besides the GLOBE DEM, associated files include a source/lineage file. This source/lineage file provides a mask of ocean coverage (by using category 0 of the source/lineage file), so that the user may reassign the -500 flag values for ocean coverage to 0, then later re-separate those values from 0 values on land.
Due to the nature of the raster structure of the DEM, small islands in the ocean less than approximately 1 square kilometer (specifically, those that are not characterized by at least one 30" grid cell and/or do not have coastlines digitized into Digital Chart of the World or World Vector Shoreline) may not be represented.