elevation

Elevation is the height of a point above a reference level, most commonly mean sea level. It is used to describe how high a location sits on the Earth's surface and can be expressed as absolute height above a datum or as a relative height compared with another point. In everyday language, elevation often means height above ground level, but scientifically the reference datum and its conventions determine the measured value.

Measuring elevation involves several methods. Traditional surveying uses leveling and triangulation to determine relative heights. Global navigation satellite systems (GNSS), such as GPS, provide ellipsoidal heights referenced to a mathematical reference ellipsoid. To express elevation above sea level, ellipsoidal heights are converted using geoid models to obtain orthometric height, which accounts for the uneven gravity field. The relationship is H = h − N, where H is elevation above the geoid (MSL), h is ellipsoidal height, and N is geoid undulation.

Data products include digital elevation models (DEMs) and contour maps that illustrate terrain relief. Elevation data support cartography, hydrology, civil engineering, urban planning, forestry, and aviation, enabling flood models, slope analysis, and site selection.

Common examples include Mount Everest, often cited as about 8,848 meters above mean sea level, and areas below sea level such as Death Valley. Elevation can vary with tides, crustal movement, and changes in reference datums, so precise values depend on the chosen datum and model.