Pie Chart Guide

When to use a pie chart

A pie chart is a familiar way of showing proportions. For example, the pie chart below shows the proportions of a budget for advertising: 50% television, 40% newspaper, and 10% yelling on a street corner. The percentages are encoded are "slices" of a pie, with the area corresponding to the percentage.

How our pie chart works

The Many Eyes pie chart shows each slice in a different color. You don't need to put your numbers in percentage form: the visualization does this for you. (In the process it ignores any numbers that are negative or missing.) You can move the mouse over slices for more information on each one.

You can also select slices by clicking on them or by clicking their names in the legend. The slice is then shifted out from the center to highlight it. This is useful if you wish to make a comment about a particular slice: the highlighting will be bookmarked along with your comment. If you control-click, you can select more than one slice at a time, and the visualization will tell you the proportion of the total items selected.

Data requirements

The pie chart needs one column of text, for labeling slices, and at least one numeric column for slice values. In the configuration sandbox you can specify more than one numeric column, in which case viewers can use a menu to switch between different numeric values. You might want multiple numeric columns if you are looking at poll results from multiple years.

A sample data table in the pie chart format is:

Expert notes

Pie charts have a mixed reputation. They are popular in business and the media but many information designers have criticized the technique. Some claim that the pie slice shape communicates numbers less exactly than other possibilities such as line length. But this remains unclear in the context of proportions: for example, we have seen no studies that looked at the task of judging whether an item is more or less than 50%. It's also unclear whether exact communication of numeric values is the only evaluation criterion; at least one study indicates that use of a pie chart for analyzing a problem as opposed to a bar chart changes the way people think about the problem.