We learn how to represent the data on the bar graph.
Data can be represented by bars (like rectangle) whose lengths represent numerical values. One can use horizontal or vertical bars. Instead of rectangles one way even use line segments in such graphs.
To represent different numbers, first we need to decide what number a unit length of the bar represents. For example, if the data is of the population of villages, we can choose 1 cm of the bar to represent 500 people. This relation between the unit length of the bar and the quantity it represents is called the scale of the bar graph. The chosen scale is sometimes mentioned in the bar graph. In this case, the scale would be written as 1 cm : 500 people.
One can choose any scale for a graph. Obviously, the scale should be such that all the base of the graph fit on the paper on which it is drawn.