Map projection is the process of transforming angular (spherical / elliptical) coordinates into planar coordinates. All map projections introduce distortion (e.g., to areas, angles, distances) in the resulting planar coordinates. Understanding what, where, and how much distortion is introduced is an important consideration for spatial computations and visual interpretation of spatial patterns, as well as for general aesthetics of any map.
Devised by Eratosthenes of Cyrene, geographic coordinate systems date back to the 3rd century BCE and have been used in mapping locations over the globe ever since. Latitude and longitude, or geographic coordinates, are the kernel of a geographic coordinate system. However, such a system is abstract unless anchored to the Earth in some way. The geodetic datum, or terrestrial reference frame as it is now called, comprises the anchor. Geographic information systems make extensive use of geographic coordinate systems to uniquely georeference spatial data. Here it is important to understand the uncertainty of a georeferenced ground position, given in latitude and longitude, as a function of the number of decimal places specified. Geocoding is a widely used application of geographic information systems that converts between street addresses and coordinates.