Elevation histogram of the surface of the Earth – approximately 71% of the Earth's surface is covered with water.

The elevation of a geographic location is its height above a fixed reference point^{[citation needed]}, 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.

  Maps and GIS

  Part of a topographic map of Haleakala (Hawaii), showing elevation.

  Landsat Image over SRTM Elevation by NASA, showing the Cape Peninsula and Cape of Good Hope, South Africa in the foreground.[2]

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.

  Hypsography of the Earth. Notice that Earth has two peaks in elevation, one for the continents, the other for the ocean floors.

  Temperature

  Vertical Distance Comparison

Temperature is less in areas of higher elevation, approximately 6.5 degrees Celsius cooler per 1000 meters.^[1] This is due to less density of air at higher altitudes.

  See also

Look up elevation in Wiktionary, the free dictionary.

• Altitude
• Geodesy
  • Geodesy of North America
    • Sea Level Datum of 1929 later National Geodetic Vertical Datum of 1929 (NGVD 29)
    • North American Vertical Datum of 1988 (NAVD 88)
• List of European cities by elevation
• List of highest mountains
• List of highest towns by country
• Normaal Amsterdams Peil
• Normalhöhennull
• Physical geography
• Summit (topography)
• Table of the highest major summits of North America
• Topographic isolation
• Topographic map
• Topographic prominence
• Topography
• Vertical pressure variation

  References

  External links

• U.S. National Geodetic Survey website
  • Geodetic Glossary @ NGS
  • NGVD 29 to NAVD 88 online elevation converter @ NGS
• United States Geological Survey website
• Geographical Survey Institute
• Downloadable ETOPO2 Raw Data Database (2 minute grid)
• Downloadable ETOPO5 Raw Data Database (5 minute grid)
• Find the elevation of any place
• ELEV

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