GEOGRAPHIC INFORMNATION SYSTEMS Lecture 10: State Plane Coordinate System

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1 State Plane Coordinate System GEOGRAPHIC INFORMNATION SYSTEMS Lecture 10: State Plane Coordinate System Why do we need the State Plane Coordinate System? - the SPCS was designed as a state by state rectangular coordinate system - like UTM, the system was designed to overcome the difficultly of calculating distances and areas How it works - the SPCS was established in the 1930 s by the U.S. Coast and Geodetic Survey - the system was designed to facilitate surveys and mapping within a state - the SPCS is a projected coordinate system - like UTM, the SPCS ignores the curvature of the Earth over a small area - each state is divided into one or more zones - the number of zones depends upon the size of the state (some states have only one zone) - for the largest states, Texas has 5 zones, California has 6 zones and Alaska has 10 zones - in Texas the 5 zones are designated as North, North Central, Central, South Central and South - each state or zone within a state is projected - the projection used is either a transverse Mercator (for N-S zones) or a Lambert conformal conic (for states with E-W zones) - a rectangular (Cartesian) coordinate system is then applied to the map area (the state zone) - in some states the zones run north-south - to minimize distortion, these states use a transverse Mercator projection for each zone - a central meridian runs north-south down the center of each zone in the state - in some states the zones run east-west - to minimize distortion, these states use a Lambert conformal conic projection for each zone - the standard parallels run east-west through the each zone in the state - in Texas, the zones run east-west so Texas uses a Lambert Conformal Conic projection - the SPCS provides a linear accuracy of 1 unit in 10,000 (about 6 inches a mile) - in the 1930 s, 1 in 10,000 was considered the limit of survey accuracy - it is 4 times more accurate than UTM, which has a accuracy of 1 in 2,500 (about 2 feet in a mile) Horizontal Datums and Units - SPCS is usually referenced to either NAD_27 or NAD_83 - when the SPCS is referenced to NAD_27, the system was designed to use English units (feet) - when referenced to NAD_83, the system was designed to use metric units (meters) although these metric units are often converted to feet - in the U.S., most cadastral and engineering applications use the SPCS in feet referenced to either NAD_27 or NAD_83 - the easting is measured east of a line located west of the zone border - the northing is measured north of a line located south of the zone Describing Coordinates - recognize that a coordinate can be replicated in different states and in different zones within a state - to describe a coordinate, you must specify the datum, state and zone, and measurement units - e.g. NAD 27, Texas Central Zone (4203), easting: 2,818,560 feet E, northing: 230,591 feet N - also note that the State Plane Coordinate System is not a global coordinate system (like UTM) - it only applies in the United States - including Alaska, Hawaii and Puerto Rico - in other parts of the world, most countries have developed similar systems for their own use Copyright 2015, Kevin Mulligan, Texas Tech University

2 State Plane Coordinate System on Topographic Maps (in lab) - know how the state plane coordinate system works - know how to find state plane coordinates on a topographic map Copyright 2015, Kevin Mulligan, Texas Tech University

3 Copyright 2015, Kevin Mulligan, Texas Tech University

4 Last Time GIST 3300 / 5300 Projected Coordinate Systems Universal Transverse Mercator (UTM) Coordinate System - why do we need the UTM coordinate system? - how does it work? - UTM coordinate system on topographic maps

5 Today GIST 3300 / 5300 State Plane Coordinate System Projected Coordinate Systems - why do we need the State Plane Coordinate System? - how does it work? - State Plane coordinates on a topographic map

6 State Plane Coordinate System Why do we need the State Plane Coordinate System? - trying to address the same problem as the UTM coordinate system - uses the same basic approach - for a small area, we can ignore the curvature of the Earth and apply a rectangular (Cartesian) coordinate system Y axis x 2,y 2 C B x 1,y 1 A x 2,y 1 We can use this approach if the units are planar (ft or m). We can not calculate distances and areas if the coordinates are expressed in degrees. X axis

7 State Plane Coordinate System Why do we need the State Plane Coordinate System? - we could use the UTM coordinate system for state-wide mapping - but many states cover more than one UTM zone

8 State Plane Coordinate System How does it work? - the SPCS system was established in the 1930 s - by the U.S. Coast and Geodetic Survey - system designed to facilitate surveys and mapping at the state level - uses a rectangular (Cartesian) coordinate system over a small area - like UTM, the SPCS ignores the curvature of the Earth within a zone - hence the name state plane - allows us to use plane geometry or plane surveying techniques - provides linear accuracy of 1 unit in 10,000 units (roughly 6 in in a mile) - in 1930 s, 1 in 10,000 was considered the limit of surveying accuracy - SPCS is four times more accurate than UTM (1 linear unit in 2,500 or 4 units in 10,000 roughly 2 feet in a mile)

9 State Plane Coordinate System How does it work? California 6 zones Texas 5 zones Comparison of State Plane and UTM Zones

10 State Plane Coordinate System (SPCS) To minimize distortion - states with zones that run north-south use a Transverse Mercator projection - central meridian through the center of each north-south zone - states with zones that run east-west use a Lambert conformal conic project - standard parallels through the center of the east-west zone

11 State Plane Coordinate System

12 State Plane Coordinate System - the Capital Dome in Austin

13 State Plane on Topographic Maps Full values shown in lower left and upper right on map State Plane Black Ticks

14 State Plane Horizontal Datums and Units United States - because the SPCS is a coordinate system designed for use in each of the U.S. states, it is usually referenced to either NAD 27 or NAD 83 - when referenced to NAD 27, the system uses English units (feet) - when referenced to NAD 83, the system was designed to use meters but English units can be used as well - most widely used in local cadastral surveys and engineering applications Other Parts of the World - the State Plane Coordinate System applies only in the U.S. - many other countries and provinces have their own system

15 State Plane Describing Coordinates - recognize that a single coordinate (an easting and northing) can be replicated in different states and different state zones - to describe a complete State Plane coordinate, you must specify: 1) the datum 2) the state and zone within the state 3) the easting and northing 4) and the measurement units (feet or meters) Example: NAD 27, Texas Central Zone, 2,818,560 feet E, 230,591 feet N