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: Mercator Distance: 3, miles
Projection: Albers Equal Area Distance: 2, 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
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)
Latitude (equator)

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)
X>0
Y>0
X<0
Y<0
(0,0) Y X

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