How to Measure Distances on a Map

Use a Ruler, or Curvimeter, or Even Google Maps Distance Calculator.

If you want to calculate the real world distance of a route, you need first to measure the equivalent distance on the map. This step is simple if the route is a straight line between two points. All you need to do is to measure the distance with a ruler. If you don't have a ruler, bear in mind that usually there are inscribed rulers in the base plates of orienteering compasses. Another way is to use drawn grid lines across the maps as measuring tool. The grid lines form an array of identical squares with sides of a specific length. After figuring out the dimensions of one square, the grid effectively becomes a ruler. For more complex routes, divide your route into straight-line segments and measure the distance of each segment one by one. Simply add the length of all segments to calculate the total length of the route.

Scale of a Map

Three Types of Map Scale.

All maps or charts are drawn to a specific scale. The scale is the relationship between a distance on the map versus the same distance in the real world. A large-scale map shows a small area in great detail, while a small-scale map covers a large area but with little detail. Selecting a map with an appropriate scale is therefore a compromise between coverage and detail, and depends on your intended activity. For example, climbing a mountain with complex topography requires a large-scale map, while a small scale map may be a better choice for a long canoe trip. The scale that you see written on the map is just an approximation. It is never completely constant across the whole map, but varies according to the projection that was used to create the map. The larger the area that a map covers, the more susceptible it is to scale variations. The scale can be expressed as a verbal scale, a ratio scale, or a bar scale.