StatePlane_CoorSys

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he State Plane Coordinate System

bbreviated as SPS or SPCS ) is extremely popular among state and localovernments. Its popularity is primarily due to its accuracy -- in terms of linear measurements four times as accurate as the Universal Transverse Mercator (UTM) system. However, ithieves this accuracy through the use of relatively small zones, and these small zones can be

uite a problem in mapping projects covering larger areas. Because of this limitation, the statane system has never really caught on for regional or national mapping tasks.

he history of the state plane coordinate system goes back to sometime around 1930, when angineer from the North Carolina state government (there are conflicting stores about exactlyho this engineer was, and what state agency he worked for) approached the U.S. Coast andeodetic Survey office. The U.S. Coast and Geodetic Survey has since been split into twogencies, the Office of Coast Survey (OCS) and the National Geodetic Survey (NGS), both of hich are located within the National Oceanic and Atmospheric Administration (NOAA). Theffice of Coast Survey has primary responsibility for developing maritime charts and otheravigational aids for U.S. seaports, while the National Geodetic Survey is responsible (along we U.S. Geological Survey), for creating and maintaining survey control points for lands withi

r controlled by) the United States (survey control points are things like the monuments useentify the initial points and secondary points used in datums)1. The Coast and Geodetic Surthe agency founded by Ferdinand Hassler, the same guy who came up with the first comple

escription of the polyconic projection.

any rate, sometime around 1930, an engineer from the North Carolina state governmentpproached the Coast and Geodetic Survey Office and inquired about the possibility of usingmple techniques to survey the entire state. The simple techniques that the engineer wantedse ignore the curvature of the Earth and instead assume the Earth's surface is simply a flatane (for this reason, these simple techniques are called plane urveying techniques ). Plane surveyinchniques use Cartesian coordinates, and require nothing more than simple Euclidean geomeve always had the impression that this engineer was either lousy with math or just plane la

ut I'm probably being unfair).

you've gone through the previous learning guides, you know that it isn't possible to flatten rved surface of the Earth into a flat plane without distorting the surface in one way or anothat the engineer was requesting was a spatial coordinate system with no distortion, a

s mathematically impossible to create such a system. However, the North Carolina engineer

vidently wasn't aware of this fact, so my guess is that he left the Coast and Geodetic Surveyfice rather disappointed that fateful day. Nonetheless, the engineer's visit led to a cooperati

enture between the Coast and Geodetic Survey and the North Carolina state government, anforts to build a North Carolina spatial coordinate system with minimal stortion was started. In 1933 this cooperative venture produced the North Carolina Coordinaystem. In less that 12 months, the North Carolina system had been copied into all of themaining states, and the State Plane coordinate system was born.

its modern form, the state plane coordinate system covers all 50 of the United States, but

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oes not extend beyond the borders of the U.S. The system is designed to have a maximumear error of 1 in 10,000. This means that if you use state plane coordinates to measure a libeing 10,000 units in length (you can use any measurement units you like -- feet, meters,

iles, cubits -- it doesn't mater), you may be off by as much as one unit (i.e., the line might bnywhere from 9,999 to 10,001 units in length). This is four times as accurate as the UTMstem, whose maximum linear error is 1 in 2,500, which, when you multiply both sides by foanslates into a maximum error of 4 in 10,000.

ke the UTM system, the state plane system is based on zones. However, while the boundariUTM zones follow lines of latitude and longitude, state plane zones generally follow politica

oundaries. First, no state plane zone spans more than one state, so all boundaries betweenates are also boundaries between state plane zone. Furthermore, given the state planestem's desired level of accuracy, many of the larger states are too big for a single state planne. These large states are divided into multiple zone (Figure 1). Generally, the boundaries

etween state plane zone within a state follow county lines. The only exception to this countyoundary rule occurs in Alaska; the counties in Alaska are so huge that it isn't possible to use

unty boundaries to define zone boundaries and still maintain the state plane system's desirein 10,000 level of accuracy. Thus, in Alaska, state plane zones fall back into the UTM patterllowing lines of latitude and longitude. All totaled, the state plane coordinate system uses

bout 120 zones to cover the entire United States.

ate plane zones whose long axis run north-to-south (e.g., Idaho West, Illinois East, or Newexico Central -- click on a few states in Figure 1 to see more examples) are mapped using aansverse Mercator projection, but unlike the Transverse Mercator projection used in the UTstem, the State Plane system uses a Transverse Mercator projection that is tangent, not

cant. State plane zones whose long axis runs east-to-west (e.g., Texas Central, Washingtonouth, and Pennsylvania South -- click on a few states in Figure 1 to see more examples) areapped using a Lambert Conformal projection. In either case, the projection's central meridiagenerally run down the approximate center of the zone. Almost all state plane zones areapped using the Clarke 1866 spheroid. The only exception to this rule involves Michigan. Inchigan, state plane zones are mapped using the rarely encountered "Michigan spheroid",hose surface is generally about 800 feet higher than the Clarke 1866 spheroid.

nce a zone is mapped, a Cartesian coordinate system is created for the zone by establishingigin some distance (usually, but not always, 2,000,000 feet) to the west of the zone's centreridian and some distance (there is no standard; each zone uses its own unique distance) te south of the zone's southernmost point (Figure 2). This ensures that all coordinates withine zone will be positive. The X -axis running through this origin runs east-west, and the Y

xis runs north-south. Distances from the origin are generally measured in feet, and just as ise case with the UTM system, X distances are typically called eastings (because they measstances east of the origin) and Y distances are typically called northings (because theyeasure distances north of the origin).

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Figure 2. The geometry of establishing an origin for the Colorado North State Plane CoordinaSystem zone.

would like to thank Mr. Dave Minkel of NOAA for setting me straight regarding the history oe U.S. Coast and Geodetic Survey.

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