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How to Understand Map Ratios

Despite the fact that there are hundreds of map projection types, no flat map can accurately represent the ratios (of sizes, shapes, distances, and directions) of the real Earth. Some projections sacrifice one or more of these traits to adhere to another. To understand how the size and shape ratios on a map work, compare a Mercator projection to a globe.

Things You'll Need

Mercator projection map
Tracing paper
Pencil
Globe

Instructions

Shape comparison
- 1
  Locate Greenland on the Mercator projection. Place one sheet of tracing paper over the island on the map.
- 2
  Trace the outline of the island onto the tracing paper using a pencil. Remove the paper from the map.
- 3
  Locate Greenland on the globe. Place your traced drawing of Greenland over the globe's representation of Greenland. Even if the ratio of the scale of the map to the scale of the globe is large, you will notice the shape distortion.
Size comparison
- 4
  Locate Alaska on the map. Place the tracing paper over it and trace the outline of the state.
- 5
  Locate Brazil on the map. Now place your tracing of Alaska over the map's representation of Brazil. Note that their areas appear approximately the same size. In actuality, Alaska is only 20% the size of Brazil.
- 6
  Place your tracing of Greenland over the map's representation of Africa. Note, again, that they appear the same in size. However, Greenland is only 7% the size of Africa.

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