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Understanding GIS Map Projections and Coordinate Systems

Discover the importance of map projections in GIS, including distortion effects and coordinate systems like Mercator and Albers Equal Area. Learn about geographic and rectangular coordinates, State Plane Coordinates, and Universal Transverse Mercator (UTM) system.

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Understanding GIS Map Projections and Coordinate Systems

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Presentation Transcript

  1. GIS Lecture: Projections

  2. Outline • Map Projections • Coordinate Systems

  3. Map Projections

  4. Map Projections and Distortion • Mathematical transformation that behaves as if it were projecting features of the world onto one of three surfaces: a plane, cone, or cylinder

  5. When Projection Is Important • Measurements used to make important decisions • Comparing shapes, areas, distances, or directions of map features • Feature and image themes are aligned New York New York Los Angeles Los Angeles Projection: MercatorDistance: 3,124.67 miles Projection: Albers Equal AreaDistance: 2,455.03 miles Actual distance: 2,451 miles

  6. When Projection Is Not Important • Business applications • Not of critical importance • Concerned with the relative location of different features • On large scale maps - street maps • Distortion may be negligible • Map covers only a small part of the Earth's surface.

  7. Coordinate Systems

  8. Projection vs. Coordinate System • Projection = the method used for flattening the paper on the spherical earth • Coordinate System = • the method for referencing specific locations • - on a sphere (Geographic Coordinates) - on that flattened paper (Rectangular Coord)

  9. Geographic Coordinates • Geographic Coordinate System (GCS) • Spherical coordinates • “Un-Projected” • Angles of rotation of a radius anchored at earth’s center • Latitude and Longitude

  10. Latitude and Longitude • Longitude (Meridians) • Latitude (Parallels)

  11. Latitude and Longitude • Longitude (prime meridian) 0 • Latitude (equator) 0

  12. Latitude and Longitude • Coordinates Pittsburgh, PA USA 40°26’2”N latitude -80°0’58”W longitude 40 -80

  13. Rectangular Coordinates • Used for locating an intersection on a flat sheet of paper • Cartesian Coordinates (X,Y) Y X<0 Y>0 X>0 Y>0 (0,0) X X<0 Y<0 X>0 Y<0

  14. State Plane Coordinates • Used by local US Governments • All positive coordinates in feet

  15. State Plane Coordinates • Zones • 125 zones, following state and county boundaries • At least one for each state

  16. City of Pittsburgh as Geographic Coordinates

  17. City of Pittsburgh as State Plane Coordinates

  18. Universal Transverse Mercator (UTM) • Coordinate system used by U.S. Military • Covers entire world • Metric coordinates

  19. How do I know what my data is?

  20. Summary • Map Projections • Coordinate Systems

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