What is a pie diagram useful for?

Concept

A pie diagram (pie chart) is a circular statistical graphic divided into slices. Each slice's angle (and area) is proportional to the quantity it represents out of the total, so a pie diagram shows how a particular category's amount relates to the whole -- not raw comparisons, not trends, and not chronology.

Application

A pie chart treats the full data set as one whole -- 360 degrees or 100% -- and gives every category a slice sized to its share of that total. A category that is 25% of the total occupies 25% of the circle. This is precisely the description "showing a particular amount in relation to the whole," which is why that is the correct option.

Cross-check

The remaining options describe other chart types, not a pie diagram:

• Comparing different amounts side by side is what a bar or column chart does, using bar length/height rather than a share of a circle.

• Showing a pattern or trend across a sequence (such as time) is the role of a line graph, which plots successive points rather than proportional slices.

• Showing features of a historical period is the role of a timeline, not a statistical proportion chart.