Reading a bar graph

A bar graph shows data with bars of the same width, with equal gaps between them. The length (or height) of each bar stands for a number. Like a pictograph, a bar graph has a scale telling what one unit of length stands for. Lakhanpal draws absent students as bars with 1 unit = 1 student, so a bar 7 units long means 7 students were absent.

The traffic police count the vehicles passing a busy crossing in Delhi each hour from 6 a.m. to noon. Here 1 unit = 100 vehicles.

• The longest bar, for 7–8 a.m., is 12 units: 12 × 100 = 1200 vehicles, the heaviest traffic. That tells the police when to send the most officers.
• 8–9 a.m. is 10 units: 1000 vehicles.
• 9–10 a.m. is 8 units: 800 vehicles.

Bars can be combined. From 8 to 10 a.m. is two hours, so add the two bars: 1000 + 800 = 1800 vehicles.

Another graph shows the population of India from 1951 to 2001, in crores. One unit per person would be impossible, so 1 unit = 10 crores. A bar of 5 units is 5 × 10 = 50 crores; a bar of 8 units is 80 crores. Always read the scale before you read a bar.