Engaging viewers with interesting depictions of data always bears the risk of creating misleading or unreadable graphics. The square pie chart (or waffle chart) strikes a good balance between being interesting and not distorting the data. Here is an argument for the power of the pie and against the boredom of the bar.
The above chart was used in a series of articles on debt in the US in the New York Times. While not strictly a square pie chart, it does illustrate its main features: it’s visually interesting, very readable and discoverable, and it does not distort the data.
Showing the same information in a bar chart may have been more “standard,” but also rather dull. In addition, the differences between the values would have made it difficult to compare them. The matrix chart above lets the viewer easily work out how many times the average savings is owed in mortgages and other debt.
The chart also makes a point: that the savings are a tiny fraction of the debt. There is really no way not to see that. And that is visual communication beyond simple data visualization. A bar chart would not be able to do that, unless it essentially claimed that the savings were zero.
Kaiser at Junk Charts criticized the following chart (New York Times magazine, April 27, 2008):
He offered a bar chart as an alternative, which worked in this case because the values are not that far apart. But it was also as dull as any other chart, with nowhere near the visual interest of the “brick chart.”
I actually think that this chart is quite clever. It uses a 10×10 grid as the base, so it is easy to read the numbers from looking at the number of layers. Despite the pseudo-3D and the fact that parts of the chars are occluded, the exact numbers can be read quickly. And the red brick metaphor even has a certain resemblance with school buildings.
In short, the chart has a style and a message. Good charts do not only have to be correct, they also have to be appealing. And this is well done here.
There is also a collection of good examples of pie charts in business graphics. Some of them may be a bit overloaded, but compared with other sins committed in business graphics and dashboards, it’s very tame. I’d take a matrix/waffle/square pie chart over gauges and artificial horizons any day. Perhaps the influence of treemaps in business also helps make these charts look more familiar and thus more acceptable.
There is no doubt that we need to be careful about the choice of visual representation, and that we need to encourage the use of good charts and criticize the bad ones. But that doesn’t mean we can get lazy and squeeze everything into a few standard charts types we’ve been using for decades. That is especially true if we want people to actually care about what we’re trying to show – and not bore them to tears.