Information systems may be broadly divided into nonspatial and spatial categories. Most information systems, including management information systems, do not refer their data to a spatial coordinate system. For example, payroll records are usually linked to a person rather than a specific location. Spatial information systems refer data to some coordinate system. For example, architectural software records the spatial relationship of beams to the foundation of a building but not necessarily to the location of the beams or the building on Earth's surface. Geographic information systems (GISs) are a subset of spatial information systems that do refer information to location.

Locations in a GIS are usually referred either directly or indirectly to coordinates denoted by latitude, longitude, and elevation or depth—or some projection of these onto a flat surface. The sciences of geodesy (concerned with the size and shape of Earth and the...