geometry

A map feature geometry is information relating to its shape (line, polygon, raster, and so on) and position.

GeoTIFF format

GeoTIFF represents an effort by over 160 different remote sensing, GIS, cartographic, and surveying related companies and organizations to establish a TIFF based interchange format for georeferenced raster imagery.

GPS

Global Positioning System. Worldwide radio-navigation system formed from a constellation of satellites and their ground stations.

GTOPO30

GTOPO30 is a global digital elevation model (DEM) with a horizontal grid spacing of 30 arc seconds (approximately 1 kilometer). It covers the full extent of latitude from 90 degrees south to 90 degrees north and the full extent of longitude from 180 degrees west to 180 degrees east. The vertical units represent elevation in meters above mean sea level. In the DEM, ocean areas are masked as "no data" and are assigned a value of -9999.