Planar coordinates and map projections

Planar coordinate systems are independent of any particular map projection—you can use them with any projection you like. The choice of projection is not irrelevant, however, and specialized coordinate systems (like the Universal Transverse Mercator and State Plane Coordinate systems) are based on conformal projections. The reason has to do with the distance and direction calculations mentioned in the previous concept.

Since a conformal map preserves local angles, directions are not distorted (at least not at large scales) as they would be on other projections. Distance calculations are distorted, but this is true of other projections, too, since no projection preserves true scale everywhere on the map.

The coordinate systems you'll read about next are divided into zones, each with its own origin and axes. This controls distortion because each grid is applied to a limited spatial extent for which the projection parameters have been optimized.