Bar Charts

1What a bar chart shows

• Each bar stands for one category, such as one class.
• The height (or length) of the bar shows the frequency.
• All the bars have the same width, and there are equal gaps between them, to show that the categories are separate.
• For categories like classes or fruits, the bars can go in any order.

2Drawing a bar chart

Here are the seedlings planted:

1. Write a title: "Seedlings planted by each class on umuganda day".
2. Draw two axes. Put the categories (the classes) along the horizontal axis.
3. Choose a scale for the vertical axis. It must start at 0 and go past the biggest value, 50. Steps of 10 work well.
4. Label both axes.
5. Draw each bar up to its value, with the same width and equal gaps.

3Reading a bar chart

4Watch the scale

If the vertical axis started at 20 instead of 0, P3's bar would be only 5 units tall and P6's 30 units tall. P6 would look six times bigger, when really it planted only twice as many. Always start the scale at 0, and always check the scale when you read someone else's chart.

Try it yourself

P6 pupils chose their favourite fruit: mango 12, banana 9, avocado 7, orange 4.

1. What scale would suit the vertical axis of a bar chart of these results?
2. How many pupils chose a fruit?
3. How many more pupils chose mango than orange?
4. Which fruit's bar would be the second shortest?

Answers

1. Steps of 2 from 0 up to 12 (or steps of 5 from 0 up to 15).
2. 12 + 9 + 7 + 4 = 32.
3. 12 − 4 = 8.
4. Avocado (7). Orange (4) is the shortest.