Everest is the highest peak, but Chimborazo reaches farthest from Earth's centre
Mount Everest has the greatest elevation on Earth, yet the summit of Chimborazo sits farther from the planet's centre. The reason is the equatorial bulge. Elevation is measured not from the core but from a modelled sea level, and every country picks its own zero point.
A location's elevation is its height above or below a fixed reference, usually a geoid, a mathematical model of sea level treated as a surface of equal gravitational potential. Geographers keep the word for points on the ground; for things above it, like an aircraft or an orbiting spacecraft, they say altitude or geopotential height, and below the surface they speak of depth. Because Earth swells at the Equator, height above sea level and distance from the centre rank peaks differently, which is why Everest and Chimborazo each hold a record.
Zero is a national choice. The Netherlands uses the Amsterdam Ordnance Datum, known as NAP, Germany uses Normalhöhennull, literally standard elevation zero, and the United States replaced its Sea Level Datum of 1929 with the North American Vertical Datum of 1988, with online tools to convert between them. Aviation has its own rule: the International Civil Aviation Organization defines an aerodrome's elevation as the highest point of its landing area, usually given in feet on approach charts and distinct from altitude or height.
Topographic maps are the classic way to show elevation, typically with contour lines. Geographic information systems store and analyse such data digitally, most often as digital elevation models, grids in which each cell holds a height, or as digital terrain models. Global datasets include GTOPO30 and the older ETOPO2 and ETOPO5 grids, spaced at two and five minutes of arc.
In the United States, the Geological Survey's 3D Elevation Program is gathering high-quality LiDAR data across the lower 48 states, Hawaii and US territories to meet growing demand for precise terrain information. It offers three seamless national bare-earth layers at resolutions of one-third, one and two arcseconds. The word elevation also turns up elsewhere: as another name for a hill, and in architecture for a building's façade.
Source: Elevation
