A map is always smaller than in real life. The map is a miniature view of reality. The link in size between the map and the reality is called the map scale. The map scale is the ratio which compares a measurement on a map to the actual distance between locations identified on the map.
Using a map scale is important when you are trying to determine the actual distance represented on a map. Most map scales are in terms of kilometres per centimetre. The ratio between kilometres and centimetre will depend on how large an area the map is representing.
For example, a map of the Netherlands will have a much smaller scale than a map of a city, because the map of the city will show much greater detail.
In bar A, one centimetre is four kilometres ( scale 1 : 400 000 ).
In bar B, one centimetre is six kilometres ( scale 1 : 600 000 ).
In bar C, one centimetre is two kilometres ( scale 1 : 200 000 ).
In bar D, one centimetre is twenty kilometres ( scale 1 : 2 000 000 ).