A coordinate transformation is a calculation that converts coordinates from one system to another. Coordinate transformations are needed in GIS because data often have different projections, coordinate systems, and datums. To perform analyses, all data must overlay accurately in coordinate space.

A coordinate transformation might be as simple as shifting each coordinate in one or two directions, for example, x and y, by a specified distance. This is sometimes done when GIS data are just slightly off in a particular direction. Coordinate transformations can also be very complex, such as when data are in different projected coordinate systems with different datums. In this case, it may be necessary to shift, rotate, warp, and scale the coordinates using more than one kind of coordinate transformation. In most ...