Elevation

For other uses, see Elevation (disambiguation).
File:Earth elevation histogram 2.svg
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 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.

File:Earth surface NGDC 2000.jpg
This image was generated by NOAA from digital data bases of land and sea-floor elevations on a 2-minute latitude/longitude grid (1 minute of latitude = 1 nautical mile, or 1.853 km). Assumed illumination is from the west; shading is computed as a function of the east-west slope of the surface with a nonlinear exaggeration favoring low-relief areas. A Mercator projection was used for the world image, which spans 390° of longitude from 270° West around the world eastward to 120° East; latitude coverage is ±80°. The resolution of the gridded data varies from true 2-minute for the Atlantic, Pacific, and Indian Ocean floors and all land masses to 5 minutes for the Arctic Ocean floor.

Less commonly, elevation is measured using the center of the Earth as the reference point.[citation needed] Due to equatorial bulge, there is debate as to which of the summits of Mt. Everest or Chimborazo is at the higher elevation,[citation needed] 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

File:Topomapcropped.jpg
Part of a topographic map of Haleakala (Hawaii), showing elevation.
File:Srtm ramp2.world.21600x10800.jpg
Heightmap of Earth's surface (including water and ice) in equirectangular projection, normalized as 8-bit grayscale, where lighter values indicate higher elevation.

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 1 km). It uses color and shading instead of contour lines to indicate elevation.

 N60-90, W150-180 N60-90, W120-150 N60-90, W90-120 N60-90, W60-90 N60-90, W30-60 N60-90, W0-30 N60-90, E0-30 N60-90, E30-60 N60-90, E60-90 N60-90, E90-120 N60-90, E120-150 N60-90, E150-180 N30-60, W150-180 N30-60, W120-150 N30-60, W90-120 N30-60, W60-90 N30-60, W30-60 N30-60, W0-30 N30-60, E0-30 N30-60, E30-60 N30-60, E60-90 N30-60, E90-120 N30-60, E120-150 N30-60, E150-180 N0-30, W150-180 N0-30, W120-150 N0-30, W90-120 N0-30, W60-90 N0-30, W30-60 N0-60, W0-30 N0-60, E0-30 N0-60, E30-60 N0-60, E60-90 N0-60, E90-120 N0-60, E120-150 N0-60, E150-180 S0-30, W150-180 S0-30, W120-150 S0-30, W90-120 S0-30, W60-90 S0-30, W30-60 S0-30, W0-30 S0-30, E0-30 S0-30, E30-60 S0-30, E60-90 S0-30, E90-120 S0-30, E120-150 S0-30, E150-180 S30-60, W150 S30-60, W120 S30-60, W90-120 S30-60, W60-90 S30-60, W30-60 S30-60, W0-30 S30-60, E0-30 S30-60, E30-60 S30-60, E60-90 S30-60, E90-120 S30-60, E120-150 S30-60, E150-180 S60-90, W150-180 S60-90, W120-150 S60-90, W90-120 S60-90, W60-90 S60-90, W30-60 S60-90, W0-30 S60-90, E0-30 S60-90, E30-60 S60-90, E60-90 S60-90, E90-120 S60-90, E120-150 S60-90, E150-180 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.

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

Temperature

File:Vertical distances.svg
Vertical Distance Comparison

In the troposphere, temperatures decrease with altitude. This lapse rate is approximately 6.5 °C/km.[1]