Center for Studies in Demography and Ecology

Coordinate Systems

Instructor: Matt Dunbar

Coordinate Systems, the frameworks used to reference geographic locations, are one of the most important, but least understood, topics for GIS users. This workshop begins with a thorough examination of the fundamentals of Coordinate Systems, including their four main components: map projection, ellipsoids, datums, and units of measure. With this background information, we will cover a variety of exercises exploring how Coordinate Systems are handled in ESRI’s ArcMap. Participants will leave the workshop with the know-how to answer familiar Coordinate System questions such as, “why doesn’t my data line up?”, “what projection should I use to do X?”, and “my data has no coordinate system defined…what should I do?”


Prior GIS experience, such as our Intro to GIS workshop, is highly recommended.


  • Importance of Coordinate Systems
  • Components
    • Reference Ellipsoid (Spheroid)
    • Geodetic Datum
    • Map Projection
    • Unit of Measure
  • Projection Classes
    • According to Projection Geometry
    • According to Properties Preserved
  • On-the-fly Projection in ArcMap
  • Changing a Data Frame’s Projection
  • Define Projection vs. (re)Project
  • Dealing with Common Coordinate System Problems


All Workshop Materials (.zip archive)

Additional Resources

Map Projections – A Working Manual (1987), USGS Professional Paper by John P. Snyder [pdf]
Datum Transformations in ArcGIS [web link]