
In the map at left, the cartographer noted the map scale with a phrase:
From this we can measure the length of a "square" to use in calculating the map's "Scale." The length of the square equals 1 inch. Since the map states that the square is equal to 1 mile, we can determine scale by the following:
Enter the 255 as follows:


Scale is always determined by taking map and ground measurements and breaking them to a common denominator (in this case, inches), to arrive at a comparable set of numbers. The first number (map measurement) is always "1" (which could be 1 cm., 1 m, 1 foot, 1 inch, etc.). The second number (ground measurement) is always calculated so that the resulting number equals the same unit of measurement as the "1" on the ratio (in the above example, ground scale needs to be converted to inches). This provides the representative fraction. Handy calculators are available online. Here are several examples:

David
J. Bertuca, Map Librarian, University at Buffalo. Last Modified:
25 April 2013 The materials selected above do not necessarily reflect the policies and procedures of the State University of New York at Buffalo. 