Elevation



The elevation of a geographic location is its height above a fixed reference point, often the mean sea level. Elevation, or geometric height, is mainly used when referring to points on the Earth's surface, while altitude or geopotential height is used for points above the surface, such as an aircraft in flight or a spacecraft in orbit.

Less commonly, elevation is measured using the center of the Earth as the reference point. Due to equatorial bulge, there is debate whether the summits of Mt. Everest or Chimborazo are at the higher elevation, as Chimborazo is further from the Earth's center while Mt. Everest is higher above mean sea level.

Maps and GIS
A topographical map is the main type of map used to depict elevation, often through use of contour lines.

In a Geographic Information System (GIS), digital elevation models (DEM) are commonly used to represent the surface (topography) of a place, through a raster (grid) dataset of elevations. Digital terrain models are another way to represent terrain in GIS.

To determine elevation of a place, it must be surveyed, in reference to a ground control point.



Topography
The elevation of a mountain usually refers to its summit. The elevation of a hill also refers to the summit. A valley's elevation is usually taken from the lowest point but is often taken all over the valley.