NB: This post is about the problems of pie charts and is not a criticism of the hard-working people at Hailsham Town Council.
A few years ago I came across Stephen Few’s Save the Pies for Dessert article on the perils (and general pointlessness of most pie charts).
My local town council has just provided a gift illustration for the useless pie chart in a recent newsletter.
I’ll just outline some of the numerous problems with the chart:
1. There is no indication of how much money will be spent in each category, so we don’t know the overall size of the pie (perhaps they don’t know yet).
2. There are 29 categories. This means that 29 different colours are needed in the key. For example, four shades of light blue look to same to me. I don’t know which slice refers to Hailsham Revitalization, which to Election Costs, which to Outdoor maintenance and which to Hellingly PC subsidy. I am not colour-blind, but I cannot tell the difference.
3. Some the categories are so small they can barely be seen.
4. The main thing I can decipher is most money is spent on something green, something blue and something yellow.
So what is the alternative?
In this case it would be preferable just to list the amount of money (or percentage of the budget) being allocated to each category. If a visual representation is really needed a bar chart would be preferable.
Are there any real reasons for using pie charts?
1. Some readers might understand the budget better visually, but with 29 categories they would need an incredible eyesight and and superb ability to distinguish colours.
2. They might be useful where there are a small number (<5) of categories. However, the data would probably be still be better presented as a table.
3. They can be very pretty and use up some space.
Can it done worse?
1. In black and white/ greyscale.
2. Using spreadsheet's 3D pie chart feature (It looks nice but the perspective distorts the proportions.)