The main problems with pie charts are:
1. It is difficult for humans to compare areas. So the area of the pie slices is hard to compare.
2. It is difficult for humans to compare angles. So the angle of the pie slices is similarly hard to compare.
3. Humans are much better at comparing lengths.
Amusingly, 1 and 2 above were exploited by Steve Jobs in a presentation:
Hacker News yesterday I was challenged thusly:
Re: the claim that groups of pie charts are especially awful, I have a counterexample. How would you express this more clearly without a series of pie charts?The charts in question look like this:
And, so, I give you the Pie Chart Challenge. If you truly believe that a pie chart is best then send me the chart (and its underlying data) and I will attempt to recraft it as a different, more descriptive and easier to comprehend, chart of my choosing.
If I fail (i.e. I believe that the sent pie chart is the best way to show the data), then I'll... eat humble pie.