Pie charts are popular in newspapers, in magazines, and yes, even in presentations. This post is going to talk about why you should avoid pie charts and why I believe there should be no pie charts without actual pie.
I may just like pie. Apple pie is my favorite, but I also adore chocolate pie.
Anyway, rather than just saying ‘Don’t do that’, I’ll use examples to illustrate why you shouldn’t use pie charts and should instead, use bar plots. First, a pie chart isn’t an actual look at the total number of an event, instead it shows a percentage of the total events.
In this first example, there’s 5 ransomware attacks. We can look at the visualization and say ‘It appears that the n0n-negotialbl3 attack happened the most’ but we can’t say how much because the visualization doesn’t show that. But if we use a bar plot, we get a better idea.
You might say ‘well just label the pie chart with the numbers, that helps.’ A visualization should be a model for the eyes. It should illustrate the information without having to add additional bits and pieces like labeling the pie chart would require. I can look at the Bar Plot and not only see that the n0n-negotiabl3 attack had the most attacks and see that the number of attacks without adding further information to it.
Here’s another example. This one also illustrates another problem with pie charts, that is, how hard it can be to clearly discern differences.
Looking at this, can you easily tell which host (or hosts) saw the most attacks? The fewest attacks? All of the slices look more or less the same size. I have to stare at it a while to think “Ok, maybe Host7 show fewer. Or is it Host6?” But if I use a bar plot, it’s easy to see.
It’s easy to see Host7 and Host9 had the fewest attacks and everyone else was equal.
I’m going to repeat myself. A visualization is a model for the eyes. It should let you see patterns in data without guessing. I can see the anomalies of the two attacks in the bar plot that I couldn’t easily see with the pie chart.
In summary: No pie charts without actual pie. In which case the only thing you’re illustrating is the amount of pie eaten vs the amount of pie not eaten.