latlong

Latlong, short for latitude-longitude, is a geographic coordinate system used to specify positions on the Earth's surface. A latitude value measures how far north or south a point is from the equator, while a longitude value measures how far east or west a point is from the prime meridian at Greenwich. Together, latitude and longitude uniquely identify a location within a chosen geodetic datum.

Latitudes range from -90 to +90 degrees, and longitudes from -180 to +180 degrees. They can be expressed in decimal degrees or in degrees, minutes, and seconds. For example, decimal degrees: 40.7128, -74.0060; degrees, minutes, seconds: 40° 42' 46.08" N, 74° 0' 21.6" W.

Coordinates are defined with respect to a reference ellipsoid and geodetic datum, which specify the Earth's shape and the origin of the coordinate system. The World Geodetic System 1984 (WGS84) is the most widely used global datum, notably by GPS. Regional datums such as NAD83 in North America or ETRS89 in Europe are also common, reflecting local accuracy requirements and historical measurements.

Latlong underpins many practical applications, including navigation, mapping, geographic information systems (GIS), and geocoding. It supports positioning on digital maps, route planning, and spatial analysis. Users should be aware of datum and format differences, as switching between datums or coordinate orders can introduce errors, particularly near the poles or the international date line.