Elevations

Elevations refer to the height of a point above a defined reference surface. In geography and surveying, elevation describes how high a location lies relative to a zero level, most commonly mean sea level. Elevation provides a vertical component used with maps, plans, and navigation.

Geodetic elevations come in different forms. Ellipsoidal height measures distance above a mathematical reference ellipsoid used by global navigation satellite systems. Orthometric height, often called height above the geoid, measures height above mean sea level and is the more familiar form of “elevation” on many maps. The geoid is a model of the Earth’s mean sea surface that varies with gravity, complicating direct conversion between these two measures.

Vertical datums define zero height differently by region. Examples include NAVD88 and NGVD29 in North America, and global geoid models such as EGM2008 used to convert between ellipsoidal and orthometric heights. Accurate elevation data require corrections for tides, atmospheric conditions, gravity variations, and local sea level changes.

Measurement methods include leveling and trigonometric surveys for precise height differences, and GNSS (GPS) for ellipsoidal heights. Barometric and radar altimetry provide additional elevation estimates in some contexts. Modern practice often combines GNSS-derived ellipsoidal heights with geoid models to obtain orthometric elevations suitable for mapping and engineering.

Applications span topographic mapping, civil engineering, construction, aviation, flood risk assessment, and climate science, including monitoring sea level rise and land subsidence. In architecture, elevation also denotes a drawing of a building’s exterior or interior vertical surface, used to convey design and construction details.