Graph Types: Pie Charts

October 13th, 2012

The pie chart is a frequently seen graph that uses area to compare percentages for a set of categories. Although this type of graph is based on comparing single metric for each category the display is two dimensional but sometimes even appears in three dimensions.

Pie Chart Example

An illustration of a typical pie chart style that is frequently seen in reports or presentations.


Other than familiarity with this type of display it is difficult to identify a situation where a pie chart would be a good way to display data. Pie Charts are also available in a wide range of software packages, although that isn’t really a good reason to recommend them!


The help files in R for the pie function provide the following advice:

Pie charts are a very bad way of displaying information. The eye is good at judging linear measures and bad at judging relative areas. A bar chart or dot chart is a preferable way of displaying this type of data.

The main question is why would we use two dimensions (relative area further confused by angle of the wedges) to make a one dimensional comparison?

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