In celebration of Pi Day here at BlogLESS, I'm going to say something nice about pie charts.
Sure, pie charts are overused. I agree that we, as designers, need to be very calculated when visualizing information rather than falling back on easily-created MS Excel favorites like the pie chart. But, it just seems a little, I don’t know, elitist to completely disown pie charts. There are plenty of articles begging “please don’t use pie charts” and even calling pie charts “the prime evil”. There are also lots of ideas around how we can move “beyond the pie chart.”
But since it’s Pi Day, can we discuss the merits of pie charts? Two points come to mind:
1. Practically, pie charts are appropriate for displaying data in specific situations, particularly a part in proportion to a whole and more specifically, parts that are unevenly distributed with respect to the whole.
2. Emotionally, pie charts can evoke strong feelings in certain situations, given the pie’s link to other conceptual and linguistic cliches that play on our instinctive desire for sweetness and sense of proportion and fairness.
So first, the practical bit: Pie charts can sometimes visually convey percents in a way that bar charts cannot. Take this example from Jeff Clark’s post In Defense of Pie Charts. He illustrates that they are the “visual analog of the mathematical concept of percents” with the following series of charts:
Can you easily tell what fraction of the whole is represented by A (red) ? Sure, with the scale present, and even without it you can figure out that the red bar is roughly half of the total. But is it immediately obvious ? I don’t think so. Not nearly as obvious as it is in the pie chart for the same data:
But perhaps even more importantly, I value pie charts for their ability to evoke an emotional response. The concept of dividing a pie into pieces is conceptually and linguistically something that is globally understood by humans of all ages. The ideal pie is cut in equal sections, and an unequally sliced pie (chart) plays to the tension created when things are not equal. Sweetness-seeking beings like ourselves instinctively want the big piece of pie, and if it isn’t ours we feel jealousy, or anger – “Hold on a second, who’s getting that giant piece?” Pie charts can make us feel jealous, invoking a “land grab” for the bigger piece.
When used in a situation where they need to convey a politically charged message or quickly illustrate an inequality, pie charts can be quite persuasive.