State Plane Coordinate System Projections

The State Plane Coordinate System used within the United States is not one projection but instead a set of many different projections organized by Zone. Transverse Mercator projections are the basis for the State Plane Coordinate System in U.S. States having predominately north-south extent. Lambert Conformal Conic projections are also used in many of the U.S. State Plane Coordinate System zones.


Various State Plane Coordinate System projections are listed by datum and by state in Coordinate System dialog with the two main sets of listings being for NAD27 and NAD83 datums.




Because many state plane zones use Transverse Mercator projections they are subject to the same difficulties and limitations of the Universal Transverse Mercator (UTM) system, which also employs Transverse Mercator projections. It is very important for new users to realize that each State Plane Zone is a separate projection. Due to distortion effects induced by Transverse Mercator projections the State Plane system is highly unsuited for creating maps that combine more than more State Plane zone.


The accuracy of Transverse Mercator projections quickly decreases from the central meridian. Therefore, it is strongly recommended to restrict the longitudinal extent of the projected region to +/- 10 degrees from the central meridian. [The US Army standard allows +/- 24 degrees from the central meridian].


The above recommendation is met within all State Plane zones that use Transverse Mercator projections. However, given modern computer technology the recommended limits still do not result in maps that are as accurate as could be easily created using other projections centered on and computed for the area of interest.


See the Universal Transverse Mercator (UTM) topic for a discussion of this and other problems with Transverse Mercator projections.




Like UTM or Gauss Kruger, the State Plane Coordinate System is a living fossil. It was created mostly as a reflection of the technological limitations of an earlier era. When used with skill as originally intended it still functions well in expert hands. The problem with the State Plane system (as with UTM and Gauss Kruger) is that it is constantly misused by inexpert users who do not realize the limitations built into the system.