1. Coordinate systems and projections
Laura Johnson
Cherie Aukland

2. GeoTEd Partners
Module name and number

3. Module Outline Methods of determining location Spatial Reference
Coordinate system
Datum
Projection
Module name and number

4. What Is Our Location? The question: Where am I on the earth? Answers:
Blacksburg, VA
zip code 24060
mile marker 118, I-81
Worsham field: Latitude: , Longitude:

5. Where am I?
All of the previous answered the question, but which one will help me the most?
All are forms of georeferencing, or communicating location on the earth’s surface

6. Spatial Reference
A way to communicate location that has up to three components:
Coordinate system (X, Y)
Datum (accounts for shape of the earth)
Projection (minimizes 3D -> 2D distortion in some capacity)

7. Coordinate Systems Measure X, Y from an origin point
Origin and units vary based on the coordinate system
Common systems:
UTM, Universal Transverse Mercator
Public Land Survey System (PLSS) coordinates
Latitude and Longitude (WGS84)

8. Public Survey
Public Land Survey System (PLSS) used to survey most of the Western US and Western Canada
Used to determine ownership
Doesn’t account for the curvature of the earth
Divides areas into townships, ranges, sections, and quarter sections
Coordinate systems typically in meters or feet

9. Latitude and Longitude
Geographic coordinates
Starts at the equator and the prime meridian
Units of measurement are degrees, minutes, and seconds
60 minutes in a degree
60 seconds in a minute

10. Spatial Reference
Coordinate system
Datum
Projection

11. What is a datum? Model of the shape of the earth’s surface
The earth is not a perfect sphere
Spheroid = equation attempting to model the actual shape of the earth’s surface
Spheroid
Earth’s Surface
Origins

12. What is a Datum? Datums define: shape of the earth
location of latitude and longitude of origin

13. Datums
Earth’s Surface
Datum

14. Common Datums NAD27 NAD83 WGS84
What do you think will happen if you use the wrong datum?

15. Spatial Reference
Coordinate system
Datum
Projection

16. Projections
Take a 3-D world and make it 2-D

17. Projections
Important to know what projection you are using to minimize measurement and display errors
Projections are a way of taking a 3-D object (earth) and making a 2-D object (map)

18. Errors Projections usually try to hold one of the following constant:
Conformal (keep shapes the same)
Equal area (keep areas the same)
Equidistant (keep distances the same)
No projection can achieve all three
Some use a compromise of each

19. Projections Three ways of projecting Cylindrical Conic Planar Earth
Wherever the projection surface “touches” the earth, there will be the least amount of distortion.
Earth
Earth

20. Common Spatial References
Albers Equal-area
Projection, good for large areas where area measures are important
Lambert conformal conic
Also good for large areas where visualization is important

21. Common Spatial References
Universal Transverse Mercator (UTM)
One of the most common coordinate systems and projections
Measures in meters
Has “Zones”
Great for local areas
Geographic or Cylindrical Equidistant
No projection or datum
Just has coordinates assigned
Directions true, All else distorted

22. Common Spatial References
State Plane system
Varies by state
Specifies projection, coordinates, and datum
Good for state-wide analyses
Some states have multiple coordinate systems
For example, Texas
Can use UTM, Lambert, Albers, or own projection
Good for surveying

23. Questions?
Module name and number