1. Coordinate Reference Systems Jim Graham & Alex Daniels Colorado State University Warner College of Natural Resources

2. Coordinate Reference System References coordinates to the earth Also known as CRS Always has 4 components: –Coordinate System –Units –Projection –Datum

3. Coordinate Reference Systems Coordinate System –Cartesian or Rectangular –Spherical Units Projection –Geographic or Un-projected –UTM –State Plane Datum

4. Spherical Coordinates Longitude: Degrees East or West from the prime meridian Latitude: Degrees North or South from the Equator

5. Geographic “Projection” -180°180° 90° -90° 0°0° 0°0°

6. Units Spherical: –Degrees Rectangular: –Metric: Meters, Kilometers –English: Miles, Feet –Nautical: Nautical Miles Elevation: –Metric: Meters –English: Feet

7. Projected Coordinate Systems Use projection to display 3 dimensional locations on to a surface in 2D Uses Cartesian coordinates (rectangular)‏

8. Cartesian Coordinates (Rectangular)‏ X,Y Easting, Northing Units: Miles, Meters, Feet, Nautical Miles Y North X East Cogito Ergo Sum

9. Projections Different orientations, different projections http://welcome.warnercnr.colostate.edu/class_info/nr502/lg1/lg1_master.html

10. Mercator Distortion

11. Projections There are hundreds of projections 98% of the time you will be using: –Geographic (Un-Projected)‏ –Universal Trans-Mercator (UTM)‏ –State Plane

12. The Earth is an oblate Spheroid

13. Datums There are hundreds of Datums If you only work in the US, 98% of the time you will be using: –NAD 27 –NAD 83 –WGS 84 –HARN Recommendation: “Project” everything to WGS 84

14. Summary Coordinate Reference Systems (CRS) reference coordinates to the earth They are composed of: –A spherical or Cartesian Coordinate System –Units –Projection –Datum

15. CRS in GIS Your data must have a CRS! –We can guess at units, coordinate system, and even the projection –Must find the datum! Sources: –“prj” file –Internal to file –From metadata –Over the phone, email, whatever!

16. Defining the CRS in ArcCatalog

18. Shapefile with defined CRS Units: Degree Projection: –Geographic –GCS=Geograp hic coordinate system Datum: –NAD 83

19. Shapefile without a CRS Click on “Select” Or…

20. Finding the Right CRS

22. WGS 84

23. North American Datums

24. NAD 83

25. Defining the CRS in ArcGIS ArcToolBox: Data Management Tools Projections and Transforms Feature Project Raster Project Define Projection (they mean CRS)

28. Unknown CRS

29. Incorrect CRS’s are a nightmare!

30. Changing the CRS ArcToolBox: Data Management Tools Projections and Transforms Feature Project Raster Project Define Projection (they mean CRS)