Don't Use Pie Charts
If you ask me, "Should I use a pie chart for this data?" my answer will usually be "NO."
People love their pie charts, but they really should be used sparingly and only when:
You need to show large differences in proportion
The "whole" is significant to your story
You have only 2 or 3 data points (or your data points can be grouped into 2-3 parts)
Let's say I want to show a chart of teams that have won the World Series. If I stuck with just plugging in numbers and relying on Excel's defaults, I might get this...
While the above is certainly colorful (and if I had a nickel for every time I've heard "Use more color to differentiate things..."), it couldn't be farther from an effective display of data. First, the color-coded legend makes it impossible to reference the pie chart to find out which pie slice is which. And the lack of ranked order means it will take me days to figure out if the Reds have more wins than the Twins.
The above is hardly any better. While you should always try to place labels on or next to pie pieces (legends for pie charts are almost always wrong), we can see here that the amount of and type of data is just not suited for a pie chart. While I could manually put in the number of wins for each team, Excel seems to only give you the automatic option of percentage labels. And who really cares that the A's have won 9% of all World Series? (For those raising their eyebrows, that includes wins in both Philly and Oakland.)
What all this data is demonstrating is that there is a story not being told. There is no MEANING to this data visually except that lots of teams have gone all the way. There are a thousand stories in this data, but you have to pick one and then show it. So, now let's look at a pie chart WITH MEANING...
This, obviously, is much better. Especially for New York fans. The above is a good use of a pie chart, and the story is clear. But we have lost a lot of data. Let's put that data back in without losing the core MEANING OF OUR DATA, which is that the Yankees are pretty good over the long term.
The above is certainly better, but it still forces the viewer to look multiple places and doesn't tell as complete a story in context and as effortlessly as it could. The reason is that a pie chart is just not the right format for so many pieces of data. And while it's interesting to know that the Washington Nationals won it once (this was their much earlier incarnation...), the individual team numbers are not crucial to our Bronx Bombers story. The solution?
Use a bar chart. Get rid of distracting colors, tick marks, unnecessary gridlines and most individual numbers. Without even a header or any further explanatory text, the story I'm now telling couldn't be much clearer...
12 days until opening day!
