State Plane Coordinate System
Encyclopedia
The State Plane Coordinate System (SPS or SPCS) is a set of 124 geographic zones or coordinate system
s designed for specific regions of the United States. Each state contains one or more state plane zones, the boundaries of which usually follow county lines. There are 110 zones in the continental US, with 10 more in Alaska, 5 in Hawaii, and one for Puerto Rico and US Virgin Islands. The system is widely used for geographic data
by state and local governments. Its popularity is due to at least two factors. First, it uses a simple Cartesian coordinate system
to specify locations rather than a more complex spherical coordinate system
(the geographic coordinate system
of latitude
and longitude
). By thus ignoring the curvature of the Earth, "plane surveying" methods can be used, speeding up and simplifying calculations. Second, the system is highly accurate within each zone (error less than 1:10,000). Outside a specific state plane zone accuracy rapidly declines, thus the system is not useful for regional or national mapping.
Most state plane zones are based on either a transverse Mercator projection
or a Lambert conformal conic projection
. The choice between the two map projection
s is based on the shape of the state and its zones. States that are long in the east-west direction are typically divided into zones that are also long east-west. These zones use the Lambert conformal conic projection, because it is good at maintaining accuracy along an east-west axis. Zones that are long in the north-south direction use the Transverse Mercator projection because it is better at maintaining accuracy along a north-south axis. The panhandle of Alaska, whose maximum dimension is on a diagonal, uses an Oblique Mercator projection, which minimizes the combined error in the X and Y directions.
, the state plane system's cartesian grid system and simplified calculations made spatial processing faster and spatial data easier to work with.
Even though computer processing power has improved radically since the early days of GIS, the size of spatial datasets and the complexity of geoprocessing tasks being demanded of computers have also increased. Thus the state plane coordinate system is still useful.
Originally, the state plane coordinate systems were based on the North American Datum
of 1927 (NAD27). Later, the more accurate North American Datum of 1983 (NAD83) became the standard (a geodetic datum is the way a coordinate system is linked to the physical Earth). More recently there has been an effort to increase the accuracy of the NAD83 datum using technology that was not available in 1983. These efforts are known as "High Accuracy Reference Network" (HARN) or "High Precision GPS Network" (HPGN). In addition, the basic unit of distance used is sometimes feet and sometimes meters. Thus a fully described coordinate system often looks something like: "Washington State Plane North, NAD83 HARN, US Survey feet". This information is needed in order to accurately transform data from one coordinate system to another.
is an example of this. King County
, which includes the City of Seattle
, uses the "Washington State Plane North" coordinate system, while Pierce County
, which includes the City of Tacoma
, uses "Washington State Plane South". Thus any regional agency that wants to combine regional data from local governments has to transform at least some data into a common coordinate system.
Coordinate system
In geometry, a coordinate system is a system which uses one or more numbers, or coordinates, to uniquely determine the position of a point or other geometric element. The order of the coordinates is significant and they are sometimes identified by their position in an ordered tuple and sometimes by...
s designed for specific regions of the United States. Each state contains one or more state plane zones, the boundaries of which usually follow county lines. There are 110 zones in the continental US, with 10 more in Alaska, 5 in Hawaii, and one for Puerto Rico and US Virgin Islands. The system is widely used for geographic data
Geographic data
Geographic data is about much more than electronic pictures of maps.The geographic data that describes our world allows for city planning, flood prediction and relief, emergency service routing, environmental assessments, wind pattern monitoring and many other applications.Geographic data is...
by state and local governments. Its popularity is due to at least two factors. First, it uses a simple Cartesian coordinate system
Cartesian coordinate system
A Cartesian coordinate system specifies each point uniquely in a plane by a pair of numerical coordinates, which are the signed distances from the point to two fixed perpendicular directed lines, measured in the same unit of length...
to specify locations rather than a more complex spherical coordinate system
Spherical coordinate system
In mathematics, a spherical coordinate system is a coordinate system for three-dimensional space where the position of a point is specified by three numbers: the radial distance of that point from a fixed origin, its inclination angle measured from a fixed zenith direction, and the azimuth angle of...
(the geographic coordinate system
Geographic coordinate system
A geographic coordinate system is a coordinate system that enables every location on the Earth to be specified by a set of numbers. The coordinates are often chosen such that one of the numbers represent vertical position, and two or three of the numbers represent horizontal position...
of latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...
and longitude
Longitude
Longitude is a geographic coordinate that specifies the east-west position of a point on the Earth's surface. It is an angular measurement, usually expressed in degrees, minutes and seconds, and denoted by the Greek letter lambda ....
). By thus ignoring the curvature of the Earth, "plane surveying" methods can be used, speeding up and simplifying calculations. Second, the system is highly accurate within each zone (error less than 1:10,000). Outside a specific state plane zone accuracy rapidly declines, thus the system is not useful for regional or national mapping.
Most state plane zones are based on either a transverse Mercator projection
Transverse Mercator projection
The transverse Mercator map projection is an adaptation of the standard Mercator projection. The transverse version is widely used in national and international mapping systems around the world, including the UTM...
or a Lambert conformal conic projection
Lambert conformal conic projection
A Lambert conformal conic projection is a conic map projection, which is often used for aeronautical charts. In essence, the projection superimposes a cone over the sphere of the Earth, with two reference parallels secant to the globe and intersecting it. This minimizes distortion from projecting...
. The choice between the two map projection
Map projection
A map projection is any method of representing the surface of a sphere or other three-dimensional body on a plane. Map projections are necessary for creating maps. All map projections distort the surface in some fashion...
s is based on the shape of the state and its zones. States that are long in the east-west direction are typically divided into zones that are also long east-west. These zones use the Lambert conformal conic projection, because it is good at maintaining accuracy along an east-west axis. Zones that are long in the north-south direction use the Transverse Mercator projection because it is better at maintaining accuracy along a north-south axis. The panhandle of Alaska, whose maximum dimension is on a diagonal, uses an Oblique Mercator projection, which minimizes the combined error in the X and Y directions.
History
The state plane coordinate system came into being during the 1930s. It has been revised several times since then. When computers began to be used for mapping and GISGeographic Information System
A geographic information system, geographical information science, or geospatial information studies is a system designed to capture, store, manipulate, analyze, manage, and present all types of geographically referenced data...
, the state plane system's cartesian grid system and simplified calculations made spatial processing faster and spatial data easier to work with.
Even though computer processing power has improved radically since the early days of GIS, the size of spatial datasets and the complexity of geoprocessing tasks being demanded of computers have also increased. Thus the state plane coordinate system is still useful.
Originally, the state plane coordinate systems were based on the North American Datum
North American Datum
The North American Datum is the official datum used for the primary geodetic network in North America.In the fields of cartography and land-use there are currently two North American Datums in use: the North American Datum of 1927 and the North American Datum of 1983...
of 1927 (NAD27). Later, the more accurate North American Datum of 1983 (NAD83) became the standard (a geodetic datum is the way a coordinate system is linked to the physical Earth). More recently there has been an effort to increase the accuracy of the NAD83 datum using technology that was not available in 1983. These efforts are known as "High Accuracy Reference Network" (HARN) or "High Precision GPS Network" (HPGN). In addition, the basic unit of distance used is sometimes feet and sometimes meters. Thus a fully described coordinate system often looks something like: "Washington State Plane North, NAD83 HARN, US Survey feet". This information is needed in order to accurately transform data from one coordinate system to another.
Problems
The main problem with the state plane coordinate system is that each zone uses a different coordinate system. This is not a major problem as long as one's needs are within the boundaries of a given state plane zone, as is the case with most county and city governments. However, the need to transform spatial data from one coordinate system to another can be burdensome. Sometimes a regional area of interest, such as a metropolitan area covering several counties, crosses a state plane zone boundary. The Seattle metropolitan areaSeattle metropolitan area
The Seattle metropolitan area in the US state of Washington includes the city of Seattle, King County, Snohomish County, and Pierce County within the Puget Sound region. The U.S...
is an example of this. King County
King County, Washington
King County is a county located in the U.S. state of Washington. The population in the 2010 census was 1,931,249. King is the most populous county in Washington, and the 14th most populous in the United States....
, which includes the City of Seattle
Seattle, Washington
Seattle is the county seat of King County, Washington. With 608,660 residents as of the 2010 Census, Seattle is the largest city in the Northwestern United States. The Seattle metropolitan area of about 3.4 million inhabitants is the 15th largest metropolitan area in the country...
, uses the "Washington State Plane North" coordinate system, while Pierce County
Pierce County, Washington
right|thumb|[[Tacoma, Washington|Tacoma]] - Seat of Pierce CountyPierce County is the second most populous county in the U.S. state of Washington. Formed out of Thurston County on December 22, 1852, by the legislature of Oregon Territory...
, which includes the City of Tacoma
Tacoma, Washington
Tacoma is a mid-sized urban port city and the county seat of Pierce County, Washington, United States. The city is on Washington's Puget Sound, southwest of Seattle, northeast of the state capital, Olympia, and northwest of Mount Rainier National Park. The population was 198,397, according to...
, uses "Washington State Plane South". Thus any regional agency that wants to combine regional data from local governments has to transform at least some data into a common coordinate system.