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In the visualization world, a pie chart is not a preferred visualization. In fact, most purists avoid using the circular visualization altogether. However, pie charts are easy on the eyes and can be used to visualize distributions but they should be used sparingly like speedometers. Unfortunately, for pie chart lovers, this information visualization (chart junk in this case) I stumbled upon is not going to win you any new followers.
The pie chart tries to show the top 20 most expensive keywords in Google AdWords advertising. The first major problem is the size of the pie slices with respect to the actual percentage shown in the slices. If Insurance is 24% of the pie, shouldn’t it be a quarter of the pie, not one third? I understand the graphics artist was trying to fit the text in the slice, but they’ve already made such a big pie chart, why not make it bigger so the distribution is accurate? Conveniently, this leads into my next issue with the visualization.
The other major problem I have with the pie chart is the number of slices it has. This visualization is very hard to read and doesn’t even fit on my 1280x1024 computer monitor. They should have used a horizontal bar chart; this would have made the distribution easier to read and fit on a computer monitor.
For all you pie chart enthusiasts, I’m sure you’ve died a little inside.
Discussion:
Lisa Pappas said:
Great example of when not to use a pie chart! As Stephen Few has espoused, our eyes cannot perceive size differences sufficiently in many-slivered pie charts. However, as a chart type it persists. cindi Howson, in her Cool BI class at TDWI Orlando, showed the same data in a bar chart and pie chart (albeit, not with too many wedges). By show of hands, the audience solidly preferred the pie for illustration.
Alexander 'Sandy' Chiang said:
Lisa,
I use pie charts in some of my dashboards, as well. Purists would scoff at this, but as you mentioned, people prefer looking at pie charts. However, you made a very important point in your post - there were not that many wedges. If I have to use a pie chart, I make sure there are not more than 4-5 to pie slices and the screen real estate permits it.
Alexander