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

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

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

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

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

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

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

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

Projections Different orientations, different projections

Mercator Distortion

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

The Earth is an oblate Spheroid

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

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

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, , whatever!

Defining the CRS in ArcCatalog

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

Shapefile without a CRS Click on “Select” Or…

Finding the Right CRS

WGS 84

North American Datums

NAD 83

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

Unknown CRS

Incorrect CRS’s are a nightmare!

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