When to Avoid Pie Charts

Look at why pie charts are problematic and why we should avoid them.

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The problem with pie charts

One of the most common plots used to visualize the distribution of categorical data is the pie chart. While they may seem harmless enough, pie charts actually present a problem, i.e., humans are unable to judge angles well. As Naomi Robbins describes in her book, Creating More Effective Graphs (Robbins, 2013), we overestimate angles greater than 90 degrees and we underestimate angles less than 90 degrees. In other words, it’s difficult for us to determine the relative size of one piece of the pie compared to another.

Let’s examine the data of the number of flights departing NYC by the airline using a pie chart. Try to answer the following questions:

  • How much larger is the portion of the pie for EV compared to US Airways (US)?

  • What is the third largest carrier in terms of departing flights?

  • How many carriers have fewer flights than UA?

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