Coordinate System

Is the State Plane Coordinate System a projection? How does the State Plane Coordinate System relate to projections?

The State Plane Coordinate System is not a projection. It is a coordinate system that divides the United States into over 120 numbered zones. Three conformal projections were chosen:

  1. Lambert Conformal Conic for states that are longer east-west, such as Tennessee and Kentucky
  2. Transverse Mercator projection for states that are longer north-south, such as Illinois and Vermont
  3. Oblique Mercator projection for the panhandle of Alaska, because it lays at an angle

To maintain an accuracy of one part in 10,000, it was necessary to divide many states into zones. Each zone has its own central meridian or standard parallels to maintain the desired level of accuracy. Zone boundaries follow county boundaries. Indiana is divided into two zones – Indiana East and Indiana West.