Map Scale: Measuring Distance on a Map

Map Legends Can Show Scale in Different Ways

Picture of two teenagers reading a city map in Copenhagen.
Muriel de Seze / Getty Images

A map represents a portion of Earth's surface. Because an accurate map represents a real area, each map has a "scale" that indicates the relationship between a certain distance on the map and the distance on the ground. The map scale is usually located in the legend box of a map, which explains the symbols and provides other important information about the map. A map scale can be printed in a variety of ways.

Words & Numbers Map Scale

A ratio or representative fraction (RF) indicates how many units on Earth's surface are equal to one unit on the map. It can be expressed as 1/100,000 or 1:100,000. In this example, 1 centimeter on the map could equal 100,000 centimeters (1 kilometer) on Earth. It could also mean that 1 inch on the map is equal to 100,000 inches on the real location (8,333 feet, 4 inches, or about 1.6 miles). Other common RFs include 1:63,360 (1 inch to 1 mile) and 1:1,000,000 (1 cm to 10 km).

A word statement gives a written description of map distance, such as "1 centimeter equals 1 kilometer" or "1 centimeter equals 10 kilometers." Obviously, the first map would show much more detail than the second, because 1 centimeter on the first map covers a much smaller area than on the second map.

To find a real-life distance, measure the distance between two points on the map, whether inches or centimeters—whichever scale is listed—and then do the math. If 1 inch on the map equals 1 mile and the points you're measuring are 6 inches apart, they're 6 miles apart in reality.

Caution

The first two methods of indicating map distance would be ineffective if the map is reproduced by a method such as photocopying with the size of the map modified (zoomed in or reduced). If this occurs and one attempts to measure 1 inch on the modified map, it's not the same as 1 inch on the original map.

Graphic Scale

A graphic scale solves the shrink/zoom problem because it is simply a line marked with the distance on the ground that the map reader can use along with a ruler to determine scale on the map. In the United States, a graphic scale often includes both metric and U.S. common units. As long as the size of the graphic scale is changed along with the map, it will be accurate.

To find a distance using a graphic legend, measure the legend with a ruler to find its ratio; maybe 1 inch equals 50 miles, for instance. Then measure the distance between the points on the map and use that measurement to determine the real distance between those two places.  

Large or Small Scale

Maps are often known as large scale or small scale. A large-scale map refers to one that shows greater detail because the representative fraction (e.g., 1/25,000) is a larger fraction than a small-scale map, which would have an RF of 1/250,000 to 1/7,500,000. Large-scale maps will have an RF of 1:50,000 or greater (i.e., 1:10,000). Those between 1:50,000 to 1:250,000 are maps with an intermediate scale. Maps of the world that fit on two 8 1/2-by-11-inch pages are very small scale, about 1 to 100 million.