State Plane Coordinate System
Last modified August 3, 2007
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State Plane Coordinate System (SPCS) is not a projection (also known as SPC, State Plane, and State). It is a coordinate system that divides the 50 states of the United States, Puerto Rico, and the U.S. Virgin Islands into more than 120 numbered sections, referred to as zones. Each zone has an assigned code number that defines the projection parameters for the region.
Projection can be cylindrical or conic.
Learn about Lambert Conformal Conic methodology and properties
Learn about Transverse Mercator methodology and properties
Learn about the Hotine Oblique Mercator methodology and properties
Government organizations and groups who 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 is in a common coordinate system with other databases covering the same area.
The State Plane Coordinate System was designed for large-scale mapping in 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 and mappers. The goal was to design a conformal mapping system for the country with a maximum scale distortion of one part in 10,000, then consider the limit of surveying accuracy.
Three conformal projections were chosen: the Lambert Conformal Conic for states that are longer east–west, such as Tennessee and Kentucky; the Transverse Mercator projection for states that are longer north–south, such as Illinois and Vermont; and the Oblique Mercator projection for the panhandle of Alaska, because it lays at an angle.
Learn more about the Lambert Conformal Conic projection
Learn more about the Transverse Mercator projection
Learn more about the Hotine Oblique Mercator projection
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. The boundaries of these zones follow county boundaries. Smaller states, such as Connecticut, require only one zone, while Alaska is composed of 10 zones and uses all three projections.
This coordinate system is referred to here as the State Plane Coordinate System of 1927 (SPCS 27). It is based on a network of geodetic control points referred to as the North American Datum of 1927 (NAD 1927 or NAD27).
Technological advancements of the last 50 years have led to improvements in the measurement of distances, angles, and the earth's size and shape. This, combined with moving the origin of the datum from Meades Ranch in Kansas to the earth's center of mass for compatibility with satellite systems, made it necessary to redefine SPCS 27. The redefined and updated system is called the State Plane Coordinate System of 1983 (SPCS 83). The coordinates for points are different for SPCS 27 and SPCS 83. There are several reasons for this. For SPCS 83, all State Plane coordinates published by NGS are in metric units, the shape of the spheroid of the earth is slightly different, some states have changed the definition of their zones, and values of longitude and latitude are slightly changed.
Officially, SPCS zones are identified by their NGS code. When ESRI implemented the NGS codes, they were part of a proposed Federal Information Processing Standard (FIPS). For that reason, ESRI identifies the NGS zones as FIPS zones. That proposed standard was withdrawn, but ESRI maintains the FIPS name for continuity.
Sometimes people use an older Bureau of Land Management (BLM) system. The BLM system is outdated and doesn't include codes for some of the new zones. The values also overlap. You should always use the NGS/FIPS codes.
The following zone changes were made from SPCS 27 to SPCS 83. The zone numbers listed below are FIPS zone numbers. In addition, false easting and northing, or origin, of most zones has changed.
The standard unit of measure for SPCS 27 is the U.S. Survey foot. For SPCS 83, the most common unit of measure is the meter. Those states that support both feet and meters have legislated which feet-to-meters conversion they use. The difference between the two is only two parts in one million, but that can become noticeable when datasets are stored in double precision. The U.S. Survey foot equals 1,200/3,937 m, or 0.3048006096 m.
Here are two examples of SPCS 83 parameters:
|Scale Factor Reduction at Central Meridian||1:25,000||1:15,000|
|Latitude of Origin||30°30'||34°20'|
|Longitude of Origin||-85°50'||-86°00'|
Used for standard USGS 7 ½ and 15 minute quad sheets.
Used for most federal, state, and local large-scale mapping projects in the United States.