Pi Day (3/14) is next week, and once again, we are encouraging everyone in the data visualization community to use this day as motivation to help clean up ineffective pie charts within their organization or in public spaces like Wikipedia. I think there is still a mindset outside of our community that a pie chart is the embodiment of data visualization, and such thinking will continue if we don't take action when pie charts are used poorly. Replacing such a pie chart is a small but positive step to take, and we've been using #onelesspie as a moniker for the effort.
Which pie charts are ineffective or poorly used? Some would say "all of them." John Tukey and Stephen Few have gone so far as saying there is always something better that a pie chart. I detailed many ways pie charts commonly go wrong in my original call to action in 2014. However, as I argued in my keynote presentation at last year's JMP Discovery Summit conference, "all graphs are wrong," and there are always trade-offs to consider when choosing how to represent data.
I will have a pie chart makeover post to go out on Pi Day next week, but today I want to celebrate positive progress in pie chart usage. While looking around the English-language Wikipedia, I noticed that some of the less effective pie charts have been retired or have evolved into better visualizations.
Here are a few examples:
This 3D exploding pie chart was once used in the Usage Share of Web Browsers article on Wikipedia. Now it's been removed in favor of an overlaid line chart showing usage share over time.
For a number of years, the Wikipedia pages for the federal budgets of particular years featured a pie chart with way too many slices and disconnected labels (2010 budget page), but the federal budget page now has a saner pie chart with fewer wedges and better labels.