Readers, dear readers, I know my regulars are sick of hearing about how much I hate pie charts. But I came across Stephen Few’s latest newsletter – Mr. Few is a man who is a professional information graphics guru and he hates pie charts, too. Of course, he is a professional and he doesn’t use the word hate. When I saw his newsletter, a smug smile of satisfaction crossed my face and I thought to myself, “Self, maybe the readers are sick of hearing you complain about pie charts, but they might want to hear how someone else complains about them. Because: Look! He has illustrations!”.
Why pie charts are not the best choice
Think of this as graphic art for geeks, abridged from Stephen Few’s newsletter, “Save the Pies for Dessert” from his information graphics educational company The Perceptual Edge.
In the first pie chart, a person might be convinced that pie charts are a decent tool. Just look at how easy it is to see that the light green segment is 25%? Super easy. Without even thinking, it’s obvious, which is the mark of a good information graphic. As for the other segments…same problem as always. Most humans are not good at visually estimating rounded volumes.
See how easy it is to see the 25% segment here? | Stephen Few, Perceptual Edge
And what if we simply rotated the pie a little?
Pie chart rotated - much more difficult to estimate the size of the 25% segment
Now it is much more difficult to get a quick visual estimate of any of the segments, even the 25% piece and all Mr. Few did was rotate the pie. Mr. Few notes that when people use software to generate pies like this, they have little control over what piece of the pie ends up in which position. He explains that our eyes have very few visual metaphors for segmented circles, one of which is the clock: “In the earlier example, our ability to decode the green slice at 25% was assisted by the fact that the green slice began at the 6 o’clock position and extended neatly to the 9 o’clock position.”
Perhaps we solve the problem by just sticking the numerical value right near the slices of pie? He does that and then adds another layer saying, “Why stop here? ….We can solve this problem by directly labeling the slices with both the company names and the values…” which leads to this graphic:
Overly labeled pie charts | Stephen Few
But that leads him to a conclusion that I support which is that this information is much easier on the eye if it’s just in a simple table. The pie itself just confuses things.
Turning the pie into a table | Stephen Few
Much clearer in a table, no? I think so. And so does Mr. Few.
Few, Stephen. (July 2010) “Save the Pies for Dessert” newsletter for Perceptual Edge.