Thursday, November 20, 2008

Map Scales - Which is Which

Maps can be an extremely useful resource in any field based mapping project.

Associated with a map is a map scale.
The scale is the ratio of a unit of distance on the map to the equivalent distance on the surface of the earth. (For example 1:25,000 means that 1 cm on the map represents 25,000 cm on the ground, or 250 m).
A map scale is usually represented as a Ratio (1:25,000), but it can also be represented as a Fraction (1/25,000).

Maps are referred to as either 'Large Scale' or 'Small Scale' maps, which tends to cause a fair bit of confusion. Which scale is which?

Large Scale:
  • The features represented on the map appear larger. (The map covers a smaller extent of the earth).
  • The map scale, when represented as a fraction, is larger. (For example 1/1000 is a larger fraction than 1/50,000).

Small Scale:

  • The features represented on the map appear smaller. (The map covers a larger extent of the earth).
  • The map scale, when represented as a fraction, is smaller. (For example 1/1,000,000 is a smaller fraction than 1/50,000).
It should be remembered that the use of the terms, Large and Small scale, are subjective, and are somewhat dependent on the map users perspective. The principle however remains the same.

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