It is the most important map element if we want to know the meanings of coloured aspects on the Map. 

The basic difference between a map and a picture is that:
 

Using the strip method, a map area has its total strip length as 56cm and width 0.5cm. The map scale is 1:50.000. What is the area on the ground?

An area with regular shape on a map has its width as 20cm and its length as 24cm. The map scale is 1:50.000. What is the area on the ground? 

Using the SQUARES method, a map area has 18 full squares and 20 halves on a map of scale 1:50.000. What is the area on the ground?