Scales on maps represent the ratio of distance on the map to the corresponding distance on the ground. For example, 1" could be 100 miles which allows you to measure distance between two points.
you use a map scale by measuring by inches
A popular map scale used in the UK, produced by the Ordnance Survey, is 1:50 000 This means that 1 cm on the map represents 50,000 cm on the actual ground. A walker may use a map with a 1:25 000 scale. Such a scale covers a small area, but in greater detail. For instance, field boundaries, and footpaths are shown. A motorist's map may have a scale of 4 or 6 miles per inch, and will therefore show a large area, with main routes the motorist may want to use.
Here is a little trick to know how to tell the difference between a large scale map, and a small scale map. A large scale map is a map where your house would look large on it. For example, a map of your neighborhood, or a map of you area. (You can see you house on this map) A small scale map is a map where your house would look small on it (or you can't see it at all), like a map of the world, or a map of Europe. So large scale = large house small scale = small house.
It is the scale.
A map's scale measures distance. It provides a ratio of the map's distance to the actual distance on the ground. For example, a scale of 1:100,000 means that 1 unit on the map represents 100,000 units on the ground.