Viz of the Day (aka Month) – Pie Chart

So I had a lofty goal to do this every day, but building product got in the way so I took a long break.  As a result I will call this one Viz of the Month.  This time I picked the Pie Chart (includes donut 🍩) because it is controversial in the data world.  Most experts will say to never use it, but yet I see it in the wild all the time.  My guess is people like the way it looks.  So it gets points for aesthetics and therefore gets used.  

Generally speaking pies fall apart when you have more than one measure and one dimension in play.  Also that dimension better not be dense with lots of data points.  Lastly, and generally speaking, a basic bar chart will often represent the data and the variations in the data better.

Here is what you don’t want to do:

So some rules for when to use a pie?

  • Small number of data points.
  • One dimension and one measure.
  • Sum of the data should be meaningful.
  • When you want to show a total with the parts. (Donut use case)

I say use it if you want but follow the simple rules above and some basic sense of visualization style.  When looking at the charts above you can see they are way too dense to be meaningful at a glance.  If you want to know more about the dreaded pie chart and why take a look at these link, but form your own option and choose wisely.

For mobile, because of touch, we are able to make them a bit more useful by allowing users to touch and interact with the pie to easily see the details about each slice.  This style pie is available in Day by Day and Synopsis but we have a rule of less than 10 slices for our default.

Two more tips:

  1. Never do a 3D Pie! Just don’t do it, it is wrong!
  2. The best pie is Key Lime, fact!


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