Pie diagrams

A pie diagram (or divided circle) shows the parts of a total as sectors of a circle.

Each part's angle = value ÷ total × 360°; or, if the data are already percentages, angle = percentage × 3.6.

Example: if a region's land use is 40 per cent farmland, 25 per cent forest, 20 per cent pasture and 15 per cent other, the angles are 144°, 90°, 72° and 54°: together 360°.

To draw it:

• choose a radius of about 3 to 5 cm;
• draw a radius as the starting line;
• draw the angles clockwise, starting with the smallest.

Why the smallest first? If you start with the big angles, small errors accumulate, and the last, small sectors become hard to plot accurately.