# Bar Graphs

Graphical representation of data is known as bar graph. Quantity of data are represented in rectangular bars either horizontally or vertically. These bars are of uniform width with equal spacing between them.

Example

The monthly expenditure of a family is given below. Represent the data in the form of a bar graph.

 Month Jan Feb March April May Average monthly expenditure (Rs) 2500 3000 1600 3500 800

Solution

To draw the bar graph we proceed as follows.

Step 1 : Drawing the axes

Take a graph sheet. From a point O towards the left hand lower corner, draw two lines OX and OY perpendicular to each other. OX is the horizontal axis and OY is the vertical axis.

Step 2 : Labelling the axes

To make a vertical bar graph we will represent the month along the horizontal axis and the expenditure along the vertical axis
along OX write 'Month' and along OY write 'Expenditure (Rs)'. Along OX choose a uniform width of the bars, and a uniform space between them, keeping in mind the space available in the graph sheet. Here we choose 1 cm as the width of the bars and 1 cm as the space between two bars.

Step 3 : Choosing a scale

This is an important step in constructing bar graphs. If the scale chosen is too big (e.g. 1 cm = Rs. 2000 in the above example) the bars will become so small that it will be difficult to interpret the data.

On the other hand, if the scale chosen is too small (e.g. 1 cm = Rs.100), the graph will become too big and unwieldy.

In the above example, we should choose a scale in which it is possible to show the smallest expenditure of Rs 800 as well as the highest expenditure Rs 3500 with bars of suitable size.

Here we choose the scale as 1 cm = Rs.500.
On this scale

1 mm , i.e. 1 small division on the graph paper represents Rs.50
1 cm, i.e. 1 big division represents Rs.500

Step 4 : Calculating
heights of bars

The heights of bars should represent the expenditure in the month. This is calculated as follows.

(i) Jan : ( Ã— 2500) cm = 5 cm

(ii) Feb : ( Ã— 3000) cm = 6 cm

(iii) Mar : ( Ã— 1600) cm = 3.2 cm

(iv) Apr : ( Ã— 3500) cm = 7 cm

(v) May : ( Ã— 800) cm = 1.6 cm

Step 5 : Drawing the graph

Draw the five bars, each of width 1 cm, and with 1 cm space between them, with the heights as calculated above. Write the months below the bars and give the graph a title.