Locations are uniquely assigned to data in reference to coordinate systems in GIS. Georeferencing enables geospatial data of disparate sources to be integrated. The former is a relative and nonmetric method of georeferencing whereas the latter is an absolute and metric method of georeferencing. To understand coordinate systems that are used in GIS, it is necessary to understand datums and map projections. Coordinate systems used in GIS can be understood in terms of a progressive flattening of the Earth's irregular shape. Map projection is another key component of coordinate systems that must be understood. Map projection can be considered as the process of flattening the Earth's curved surface. Although the Earth is curved, most of media that represent the features of the Earth are flat. Standard GIS software comes with address geocoding. Geocoding refers to the process of turning the textual descriptions of locations to metric descriptions of locations.