A set of 124 geographic zones designed for specific regions of the United States.
The State Plane Coordinate System (SPS or SPCS) is a set of 124 geographic zones or coordinate systems designed for specific regions of the United States. It was developed in the 1930s by the U.S. Coast and Geodetic Survey to provide a common reference system to surveyors for large-scale mapping in the United States. The goal was to design a conformal mapping system for the entire U.S. with a maximum scale distortion of 1:10,000, which at the time was considered the limit of surveying accuracy. It uses a simple Cartesian coordinate system.
Depending on its size, a state contains one or more state plane zones, the boundaries of which usually follow county lines. Each zone has an assigned code number that defines the projection parameters for the region. The system is widely used for geographic data by state and local governments. Outside a specific state plane zone the accuracy rapidly declines, which makes the use of this system problematic for geographic areas that cross state (zone) boundaries.