A coordinate system is a method of defining how a file's point locations display on a map. Different types of coordinate systems exist that control how the coordinates are shown on the map. In Didger, a project can be unreferenced in Cartesian Coordinates, referenced to a geographic lat/long coordinate system, or referenced to a known projection and datum.
A Cartesian coordinate system is considered unreferenced. A local system has a location that begins numbering at an arbitrary location and increments numbers from this location.
A Geographic coordinate system uses a spherical surface to define locations on the earth. Geographic coordinate systems are commonly called unprojected lat/long. Didger has several predefined geographic coordinate systems available. Each system has a different datum. The same latitude and longitude value will plot in different locations depending on the datum.
A Projected coordinate system consists of a projection and a datum. Each projection distorts some portion of the map, based on the ellipsoid and datum specified. Coordinates can be lat/long, meters, feet, or other units. Different projections cause different types of distortion. It is recommended that you do not use projected coordinate systems if you do not need to convert between coordinate systems or if all your data are in the same coordinate system.
Map Coordinate System Overview
Introduction to Map Projections