“No Pie Charts… Not Ever!” (says I)Posted: January 11, 2008
I am a big fan of letting users drive the features of a product. In fact, we’re about to release a ranking survey based on the feature suggestions in the thousands of emails we’ve received over the past few months.
But one often-requested feature that will likely not be included in RescueTime is pie charts.
The very early mockups of RescueTime did have pie charts and I kinda liked them. They broke up the bar-chart monotony and just seemed more fun. As I continued to show and refine the mockups, it wasn’t long before crafty students of data visualization told me that pie charts were evil. It didn’t take much listening and much research to agree with them. Here are a few points for the consideration of pie-loving RescueTimers:
- Human beings are a lot better at eyeballing length than angle. If you don’t believe, check out the illustration in the sidebar of the Pie Chart Entry in Wikipedia.
- In Show Me the Numbers by Stephen Few the author says “I don’t use pie charts, and I strongly recommend that you abandon them as well.” Few says that pie charts communicate poorly. Robbins agrees. So does Tufte.
- Pie Charts (with small slices) require a legend which necessarily has visual separation from the data.
- Rotating a pie chart changes perception a bit, especially when the slices are of similar size.
- Pie Charts convey magnitude poorly. It’s difficult to eyeball the difference between a 22% slice and a 26% slice.
- When the rubber meets the road and I test pie charts with RescueTime data with Pie charts, it just conveys less meaning (with 10 slices).
All that being said, I think that we could convey the “part-to-whole” information in your usage data a lot better than we are.
So, pie-people– I’m going to do my best to comply with the spirit of your request (“we want better part-to-whole visualization!”) rather than the letter of your request (“we want pie!”). Stay tuned for it!