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"To the dull mind all nature is leaden. To the illumined mind the whole world burns and sparkles with light." -- Ralph Waldo Emerson

5.3
Map Projections

Earth's surface is curved, so plotting on a flat map is inaccurate any way you do it.
 


We will specifically look at 3 projections:
 
 

    • Mercator - standard flat map
    • Robinson – "curved" flat map
    • Conic - smaller areas


But first, a quick look at some of the basics of projecting:
 
 

When a cylinder is placed tangent to the globe, contact is along a great circle (the circle formed on the surface of the Earth by a plane passing through the center of the Earth):

 
  

In the secant case, the cylinder touches the sphere along two lines, both small circles (a circle formed on the surface of the Earth by a plane not passing through the center of the Earth):

Mercator

    Correct shapes of continents, but:
    • areas are distorted
    • longitude lines are projected parallel to each other, but
      • remember that longitude lines are not actually parallel - they meet at the poles!
    • area distortions increase as you get closer to the poles



 

Robinson

    • Similar to Mercator, but less distortion near poles. Continent shapes are foreshortened near edges and poles.
    • Longitude lines are projected curved, similar to the way they would look on a globe.

so

  • areas are less distorted near the poles than with Mercator
    •



 
 
 

Conic
Used for small areas
  • most accurate for the small area
  • points from globe projected onto cone-shaped paper later laid flat


 
 
 


 
 

In the secant case, the cone touches the sphere along two lines, one a great circle, the other a small circle:

UPDATED: 02/17/03