Compound bar and line graphs
In a compound bar graph, two or more bars are placed side by side for each year or place so that values can be compared directly. A compound line graph draws several lines on the same axes to show the trend (rise or fall) of each category. Every graph must have a title, axis labels, a uniform scale and a key (shading or colour).
- The vertical (y) axis usually shows a quantity such as output or number.
- The horizontal (x) axis shows time or place.
Pie charts
A pie chart is a circle divided into sectors. The size of each sector represents the percentage contribution of a category to the whole total.
Key idea
Sector angle = category value ÷ grand total × 360°. All the angles must add up to 360°.
For example, if rubber contributes 40 tonnes out of a total of 160 tonnes, its angle is 40 ÷ 160 × 360° = 90°. To convert to a percentage, use value ÷ total × 100%.
Interpreting the data
When interpreting, compare the highest and lowest values, identify a rising or falling trend, and work out the difference between two years. A pie chart is best for showing parts of one whole, while a line graph is best for showing change over time.