Part of a whole: the fan chart

This is a little experiment with the idea of comparing proportions of multiple entities in something that looks like a pie chart.

As you can see, an over-stylized pie chart could be reduced to an angle and displayed using a few lines, and let gestalt take care of the missing parts:

A pie chart and a simplified version as angle
A pie chart and a simplified version as angle.

The same message, no fat. And because there are no textures and arcs to deal with we can now superimpose many pies. For example, these represent proportions of the age group 65+ in 1996 (left) and 2050 (right) for 220 countries (data from the US Census Bureau). This comparison clearly shows that the World is getting older.

Superimposed lines forming angles
Superimposing multiple entities allows us to to observe the distribution of proportions.

You can see how age structures are changing in four areas of the globe. Note that, unlike pie charts, when you have more than two categories, the slices are not stacked, they all start at noon:

Small multiple representing population structure by year and continent
These small multiples show how population structure by continent is changing.

Or identify a single country (this is Portugal):

Chart displaying population structure with focus on Portugal
You can select a single country and compare it to the context.

One of the problems with pie charts is that you can compare proportions but you can’t compare wholes. In the images above we are comparing very different country sizes (Tuvalu and China?). With the fan chart we can add this dimension:

Chart combining proportions and volume
Adding population volume to the fake pie.

China and India are not helping resolution, but it would happen to any other chart. We can focus on detail:

Chart combining proportions and volume, capped for detail
You can focus on detail by capping the scale or using log scales.

These are connected scatterplots in Excel, in case you’re wondering. This is something that I suggested back in 2012 and I’m now revisiting. There are better ways of displaying the data, of course, but it’s meant to exemplify new ways of doing it, beyond the chart library, and challenge your Excel skills.

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