The elevation of a geographic location is its height above or below 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.
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.
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 1Â km). It uses color and shading instead of contour lines to indicate elevation.
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.
See also
- Height
- 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)
- Geodesy of North America
- List of European cities by elevation
- List of highest mountains
- List of highest towns by country
- Normaal Amsterdams Peil
- Normalhöhennull
- Physical geography
- Table of the highest major summits of North America
- Topographic isolation
- 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
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