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For other uses, see Elevation (disambiguation). The elevation of a geographic location is its height above a fixed reference point, most commonly a reference geoid, a mathematical model of the Earth's sea level as an equipotential gravitational surface (see Geodetic system, vertical datum). 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, and depth is used for points below the surface. Less commonly, elevation is measured using the center of the Earth as the reference point. Due to equatorial bulge, there is debate as to which of the summits of Mt. Everest or Chimborazo is at the higher elevation, as the Chimborazo summit is further from the Earth's center while the Mt. Everest summit is higher above mean sea level. Contents 1 Maps and GIS, 2 Topography, 3 Global 1-kilometer map, 4 Hypsography, 5 Temperature, 6 See also, 7 References, 8 External links, 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. Global 1-kilometer map: This map is derived from GTOPO30 data that describes the elevation of Earth's terrain at intervals of 30 arcseconds (approximately 1 km). It uses color and shading instead of contour lines to indicate elevation. Each tile is available at a resolution of 1800 × 1800 pixels (approximate file size 1 MB, 60 pixels = 1 degree, 1 pixel = 1 minute) Hypsography: Hypsography is the study of the distribution of elevations on the surface of the Earth, although the term is sometimes also applied to other rocky planets such as Mars or Venus. The term originates from the Greek word ὕψος "hypsos" meaning height. Most often it is used only in reference to elevation of land but a complete description of Earth's solid surface requires a description of the seafloor as well. Related to the term hypsometry, the measurement of these elevations of a planet's solid surface are taken relative to mean datum, except for Earth which is taken relative to the sea level. Temperature: In the troposphere, temperatures decrease with altitude. This lapse rate is approximately 6.5 °C/km.

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