State Plane Coordinate System

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If you’ve ever worked with GIS data regionally within the United States you’ve probably come across the State Plane Coordinate System.

What is the State Plane Coordinate System?

The State Plane Coordinate System (SPCS) is not a projection; rather it is a system for specifying positions of geodetic stations using plane rectangular coordinates. This coordinate system that divides all fifty states of the United States, Puerto Rico and the U.S. Virgin Islands into over 120 numbered sections, referred to as zones. Each zone has an assigned code number that defines the projection parameters for the region.

Origins

Governmental organizations or groups who do work with them primarily use the State Plane Coordinate System. Most often, these are county or municipal databases. The advantage of using SPCS is that your data will be in a common coordinate system which is the same as that of other databases covering the same area. The SPCS was created in the 1930′s by the U.S. Coast and Geodetic Survey in order to provide a common reference system to surveyors and cartographers. The SPCS is a grid system developed by USGS in 1938 for the irregular shapes of the individual US states. SPCS is widely used in public works and land surveys.

Projections

There are three possible projections for SPCS. The geometric direction of each state determines the projection utilized. For states that are longer in the east-west direction, the Lambert Conformal Conic is used. States which are longer in the north-south direction use the Transverse Mercator Projection. The panhandle of Alaska, which the sole distinction of lying at an angle, garners the use of the Oblique Mercator Projection.

Zones or FIPSZones

The main aim in creating the SPCS was to design a conformal mapping system for the entire country while maintaining a maximum scale distortion of 1 part in 10,000. In 1933 this was considered the limit of surveying accuracy. In order to attain this accuracy, the larger states needed to be divided into smaller zones or FIPS. Each zone or FIPS has its own central meridian or standard parallels to maintain accuracy. FIPS stands for Federal Information Processing Standard.

Changes from NAD27 to NAD83

The original zones were based upon a network of geodetic control points known as the North American Datum of 1927 (NAD27). With improvements within the last 50 years and the need for compatibility with satellite systems, the origin of the datum was moved and NAD83 was created. Hence ZONE refers to the older NAD27 system and FIPSZone to the newer NAD83.

SPC Utilities Page from NOAA

State Plane Codes
Lists State Plane FIPS zones as well as Adszones and UTM zones. Site created by Richard King.