1. Map Projection Properties

2. Map Projection Properties
Definition: Alterations of area, shape, distance, and direction on map projections. Why? All maps contain error because of the 3D -> 2D transformation process. How? Rendering a spherical surface on a plane causes tearing, shearing, or compression of the surface.

3. Four Map Projection Properties
Area Shape Distance Direction

4. Four Projection Properties
Major Properties
Minor Properties
Area Shape Distance Direction
Cannot exist everywhere
on map
Mutually Exclusive

5. Map Distortion
Distortions are unavoidable when making flat maps of a globe
Distortion may take different forms in different parts of the map
Few points where distortions are zero
Distortion is usually less near the points or lines of intersection where the map surface intersects the globe

6. Map Distortion
A map can show one or more – but never all – of the following at the same time:
True directions
True distances
True areas
True shapes

7. Equal Area Map Projection
A.K.A. Equivalent Map Projection Goal: Preserve area relationships of all parts of globe Identifying Marks: Meridians and parallels are not at right angles. Distance distortion is often present. Shape is often skewed.

8. Equal Area Map Projection
Useful for… General quantitative thematic maps. When it is desirable to retain area properties.

9. Cylindrical Equal-Area

10. Area
Hammer-Aitoff

11. Conformal Map Projection
Shape
Conformal Map Projection
A.K.A. Orthomorphic Map Projection Goal: Preserve angles around points and shape of small areas Same scale in all directions from/to a point. Identifying Marks: Meridians intersect parallels at right angles. Areas distorted significantly at small scales. Shapes of large regions may be severely distorted.

12. Conformal Map Projection
Shape
Conformal Map Projection
Useful for… Large-scale mapping. Phenomena with circular radial patterns (e.x. radio broadcasts, average wind directions)

13. Shape
Mercator Projection

14. Equidistant Map Projection
Distance
Equidistant Map Projection
Goal: Preserve great circle distances. Distance can be held true from one to all other points, or from a few points to others, but not from all points to all other points. Scale is uniform along lines of true distance. Identifying Marks: Neither conformal or equal area, and look less distorted.

15. Equidistant Map Projection
Distance
Equidistant Map Projection
Useful For… General Purpose Maps Atlas Maps

16. Equidistant Cylindrical
Distance
Equidistant Cylindrical

17. Azimuthal Map Projection
Direction
Azimuthal Map Projection
A.K.A. True Direction Goal: Preserve true direction from one point to all other points. Direction not true between non-central points. Useful for… Preserving direction from one point.

18. Azimuthal Equidistant Map Projection
Direction

19. Combination of Projections on a Single Projection
Equal Area
Conformal
Equidistant
Azimuthal -- No
Yes
Yes denotes they can be combined
No denotes they cannot be combined

20. Minimum Error Map Projection
A.K.A. Compromise Map Projection Goal: Simultaneously minimize all four map projection properties Useful for… General geographic cartography

21. Robinson Map Projection
Minimum Error
Robinson Map Projection

22. Organization of Cartographers for Social Equality – West Wing Clip