Editing Geographic information system (section)

===Terrain depiction===
{{main | Terrain cartography }}
[[File:Swisstopo Eiger - Grindelwald.jpg|thumb|300px|A traditional topographic map rendered in 3D]]
Traditional maps are abstractions of the real world, a sampling of important elements portrayed on a sheet of paper with symbols to represent physical objects. People who use maps must interpret these symbols. [[Topographic map]]s show the shape of land surface with [[contour line]]s or with [[Cartographic relief depiction|shaded relief]].

Today, graphic display techniques such as [[shading]] based on [[altitude]] in a GIS can make relationships among map elements visible, heightening one's ability to extract and analyze information. For example, two types of data were combined in a GIS to produce a perspective view of a portion of [[San&nbsp;Mateo County]], [[California]].
*The [[digital elevation model]], consisting of surface elevations recorded on a 30-meter horizontal grid, shows high elevations as white and low elevation as black.
*The accompanying [[Landsat]] Thematic Mapper image shows a false-color infrared image looking down at the same area in 30-meter&nbsp;pixels, or picture elements, for the same coordinate points, pixel&nbsp;by&nbsp;pixel, as the elevation information.

A GIS was used to register and combine the two images to [[Rendering (computer graphics)|render]] the three-dimensional [[perspective view]] looking down the [[San Andreas Fault]], using the Thematic Mapper image pixels, but shaded using the elevation of the [[landform]]s. The GIS&nbsp;display depends on the viewing point of the [[observation|observer]] and time of day of the display, to properly render the shadows created by the sun's rays at that latitude, longitude, and time of day.