Sorry Sir, we’re all out of pies…
Tom Brown
Perhaps you would like something else instead?
The failings of the good old pie chart are well documented, yet still they are liberally spread throughout our reports, websites and documents.
Maybe this is because of a lack of viable alternative, and an understanding of why the alternatives are more useful in communicating the information in our data.
This post offers the ‘Horizontal Ranked Bar’ (HRB) as the obvious alternative to the pie chart and explains some of the many reasons it should be used. Firstly, you should know that pie charts are only really used to present ‘Parts of a whole’ – that is where the slices of the pie add up to 100% of something, and the slices define the ‘distribution’ of a certain category within the 100%.
So why is a HRB always superior at communicating parts of a whole when compared to a pie chart? Here’s some reasons, there are more I’m sure.
Reason #1 – We’re much better at comparing length than area
It should be immediately obvious that the HRB shows the proportions between the categories more clearly than the pie – this is because we are tuned to understand differences in length more easily than area (anyone know the reason WHY this is?)
The ranking is also very clear in the HRB- its hard to tell if the pie slices are sorted in the same way (they are not).
Reason #2 – You have to use colour on a pie
Because of the design of a pie chart, you are pretty much forced to use colour to define the slices – clearly this is not true for an HRB.
This causes a number of issues; firstly, as shown here, once colour is introduced, it is likely that red and green shades will make their way onto the pie. We naturally attach a significance to these colours beyond the size of the pie slice (presumably because of stop/go traffic lights??).
Since the HRB does not require us to use colour initially, the audience must focus only on the relative lengths of the bars (as we intended).
Then, since you have to use colour on the pie, you do not get the option to use colour to display some other data. In the example below, the size of the bar is showing sales volume – but now the strength of colour is being used to show profit ratio. This allows us to display far more information on a single chart.
This also means you can’t highlight a specific category using a pie chart- notice how this works on the HRB, but three slices of the pie become one – you may want to do this to highlight the category most important to the audience.
Reason #3 – Long labels create a problem on pies
Labelling can be difficult on a pie chart at the best of times, but if you have long labels (formal country names for example) then they can render your chart unreadable – as in the example below. No such problem on the HRB – you can allow a much greater proportion of the chart space for labelling and the horizontal orientation of the chart allows for easy reading.
Reason #4 – A pie with lots of categories just doesn’t work
This is an obvious one, but worth the screen space…
Do you really need more??? Ok.
Reason #5 – You can’t add reference lines to pie charts
Ever seen an average line on a pie chart? No, what would that look like? Maybe an average slice lying around somewhere. No problem for the HRB.
Reason #6 – You can’t add variable ‘target’ lines to a pie
Ok, really an extension to #5, but important all the same. This HRB has target lines which are independent – their value is based on the category.
Reason #7 – Pie’s don’t support ‘drilling down’ well
There are many occasions when your chart should support ‘drilling down’ – splitting the chart into multiple charts in this example. The pie chart fails immediately here, whilst the HRB just keeps giving.
I’m pretty much done here – I’m sure I have missed some, please let me know if you can think of more examples – and the next time someone asks for a pie, tell them you’re all out!
Reader Comments (4)
nice! I'm doing a session at Oxford Geek Night tomorrow on this very topic. I'm tempted to throw my slides away and use yours - they're really succinct, and you cover more points than I manage! Colour and reference lines are particularly great points I hadn't considered before.
Oh well, here we go again... If you want to show proportions, you have to use a pie chart (or a donut) or something like a Pareto chart. You cannot see proportions in a bar chart. Yes, the bar chart is much more effective to show rankings and to compare data points, but that's not proportions. And you cannot easily see the total proportion of the first three data points in bar chart, for example. The problem is, we use proportions more often than we should.
No, we don't have to use colors. Yes, we can use strength of color. Yes we can use a target or a reference line (using a donut or Nightingale's rose). If you have many data points maybe you should group them.
But yes, comparing multiple pies charts is not the wisest thing to do.
@camoesjo, great comment.
After all this time, we still thrash on this? I guess if I had to choose, I would go with bars, but that's the beautiful thing. I don't have to choose! :)
see example here: pies and bars