Halvor William Sanden
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The uselessness of donut charts

Donut charts are used because they look cool, not because they are good at communicating. While being just as useless as pie charts, a donut is not just a pie chart with a hole, it’s also a distorted stacked bar biting its tail.

Hard to read

In terms of shape, there are some warning signs.

Comparing shapes

Circles are difficult to compare with each other. At a glance, it’s difficult to get an impression of any difference between two almost equal sizes, while the same change in rectangles is clearly noticeable. It’s also difficult to estimate sizes, while the same difference in a bar is more easily recognised as being half, a third or so on.

Comparing within

Round objects are difficult to read when divided into segments. Every value means a different shape at a different angle and no common level. While bars only change their length – and position if stacked.

Shapes, angles and positions

Zero is usually at 12 o’clock, but other values start where the previous one ended, like a stacked chart. But in contrast, donuts only have percentages, which means that value ticks or lines are as good as useless. The end of a segment doesn’t equal its size.

This makes every part dependant on the actual value being displayed. Which is not uncommon in charts, but you have to rely much more on reading the value to get an impression of what’s being communicated in a donut. This defeats the purpose of the chart to give a quick summary and provide information at a glance and make sizes a bit more tangible When you have to study the values, the charts become detours to the actual data.

Limited data types

The donut, like the pie, can only display certain positive percentages. They can’t handle negative values. Although I have seen people try and decide to proceed with positive values instead, which made everything wrong but it looked the way they wanted.

You always need two values. Even if there is only one number, the rest of it will be the opposite. If you are 23 per cent done, you are 77 per cent not done.

Increased percentages don’t work. A 13 per cent increase in revenue will probably look 87 per cent bad. And you can’t go past 100.

If it doesn’t make sense to have the data as percentages, you should probably not bother with calculating it either.

If you are comparing one set of numbers with another, you’re also better off with another type because there will be no common reference points.

Layout and code hell

Circles in a layout can be a fun challenge. Circles featuring unpredictable appendages is not. Donut charts require more code and more space in a layout.

Charts, in general, are difficult in a responsive setting, and they can take up a lot of space depending on the number of values and data. What donut charts can potentially save by cramming everything into it, is lost in legibility and extra space needed for labelling.

The shape itself is difficult to stack and shrink because it requires a certain size to be legible and it requires so much extra information and space around since it doesn’t have axis values.

And so the two neighbours moved in together.

Each label and value has to optimally be placed outside the shape, at a distance where it can follow its shape whatever the size and position. At the same time, it needs to not get in the way of the other values no matter their position and shape. Multiple small values next to each other is a potential headache. For developers and users.

You also need different colours. While that’s true for many charts, bars side by side can have the same colour, while things that are stacked or overlapped need to contrast each other.

What it can be used for

How much space can one value fill.

While it's almost useless from the start, both its positive and negative properties get worse with every added value. I would hardly call it a chart, illustration might also be a stretch, decor perhaps.

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