Have a slice
Even if they are not recommended, pie charts are widely used. We might come across a client or user that will not accept alternative visualizations forcing us to use them.
When this is the case, we need to make sure to make pie charts as clear and easy to use and understand as possible. There are some tips and tricks to take into account when using pie charts.
Number of slices
Pie charts are not the best choice when our data is represented by more than 10 slices. Our eye can’t distinguish what’s the biggest or smallest slice and of course we cannot tell anything about the other slices. If we cannot tell much about the slices, then the chart becomes useless.
Can you tell which is the biggest slices in the following pic chart? I can’t either, and the colors don’t help as there is no clue of what color represents the maximum or minimum value.
Now take a look at the following chart. Can you tell which is the maximum value? Most of us will say the the biggest slice is the one with darker color and we will be right most of the time. However, we will not be sure until we hover over each slice and compare the values.
Whatever the case is, it is recommended to use shades of colors. In my example, blue. This can be achieve with the ColorMix1 or ColorMix2 functions.
One simple trick consists of highlighting the biggest slice as shown in the chart below. Our eye is first drawn to the slice which is slightly out of the center of the pie. This can give as a better idea of what the biggest slice is.
Even if we have a highlighted slice with the darkest color, it can represent the smallest value.
Adding extra information
Depending on the pie chart, it is adviceable to add data points to each slice. These can be real values, or a percentage representation over the total.
Bear in mind that absolute values could be large which will make the pie smaller. Percentages on the other hand work better.
Things are getting a bit cleaner but we still need to define some order. In the previous images, we can’t tell if the slices are sorted in a particular order or not. Sorting is usually very important as allows you to follow or spot patterns. For pie charts, there is no much that can be done regarding sorting. If you have not noticed it, the previous images show a pie chart where the biggest slice is on the top left side followed by the smaller ones from left to right (counter clockwise).
You won’t notice this until you actually compare the values.
We tend to read text on rounded things in a clockwise sense. Things might change a bit if your language is read/written from right to left.
Having mentioned this, we could sort the pie chart with the highest value first (top right corner) followed by the others in a clockwise order. To make it even clearer, we can add a ranking with 1 being the highest value.
So, next time you create a pie chart, use all or some of these tips to make sure everybody is able to read and understand what you are trying to communicate. You can even mix most of them like adding percentages and ranking to provide even more information.
I would like to invite you to read a previous entry about Attribute types.