Geodesy

Overview Geodesy is the science of measuring and understanding the Earth's size, shape, gravitational field, and rotational dynamics. As the foundational discipline behind all positioning and mapping technologies, geodesy provides the reference frameworks (datums), mathematical models (ellipsoids and geoids), and measurement techniques that enable precise geographic coordinate determination. Every GPSGPSThe Global Positioning System (GPS) is a satellite-based navigation system operated by the U.S. Space Force that prov... position, every map projectionMap ProjectionMap projections are mathematical transformations that convert the three-dimensional surface of the Earth onto a two-d..., and every coordinate transformation depends on geodetic science.

Geodesy encompasses several specialized areas. Geometric geodesy focuses on the mathematical description of Earth's shape and the computation of positions on its surface, including the definition of ellipsoids and the solution of geodetic problems on curved surfaces. Physical geodesy studies the Earth's gravitational field and its relationship to the geoidGeoidThe geoid is the equipotential surface of Earth's gravity field that best approximates global mean sea level. It serv..., the equipotential surface used as the reference for orthometric heights. Satellite geodesy uses observations of artificial satellites (GPSGPSThe Global Positioning System (GPS) is a satellite-based navigation system operated by the U.S. Space Force that prov..., GLONASS, Galileo) and satellite-based techniques (satellite laser ranging, VLBI) to determine positions and monitor Earth dynamics.

Geodesy establishes and maintains global and regional reference systems that underpin all positioning activities. The International Terrestrial Reference Frame (ITRF) provides the most accurate global reference, updated periodically with new observations. National geodetic datums like WGS 84WGS 84WGS 84 (World Geodetic System 1984) is the global geodetic reference system used by GPS and most modern mapping appli... and NAD 83NAD 83NAD 83 (North American Datum of 1983) is the horizontal geodetic datum used for surveying, mapping, and navigation ac... are derived from or aligned with ITRF for practical positioning applications. Vertical datums based on geoidGeoidThe geoid is the equipotential surface of Earth's gravity field that best approximates global mean sea level. It serv... models define the reference surfaces for height measurements.

Modern geodesy supports centimeter-level global positioning through GNSSGNSSGlobal Navigation Satellite System (GNSS) is the umbrella term for satellite-based positioning systems that provide a..., monitors tectonic plate motion and crustal deformation, measures sea level change through satellite altimetry, and tracks variations in Earth's gravity field that reveal changes in ice mass, groundwater, and ocean circulation. These observations are critical for understanding and responding to climate change, natural hazards, and resource management.