A digital elevation model (DEM) is the data used by a geographic information system (GIS) to represent the shape of part of the earth's surface. It usually refers to data in raster format where each raster cell stores the height of the ground above sea level or some known datum. DEMs have wide application in geographic information science, as they can be used to model many important processes that may be dependent on surface shape. Applications include hydrological modeling, flood prediction, slope stability analysis, avalanche prediction, geomorphology, visibility analysis, radio wave propagation, three-dimensional visualization, cartographic relief depiction, and correction of remote-sensing imagery.