Make your color legend better with one simple rule
Apr 03, 2020
The pie chart about COVID-19 worries illustrates why we should follow a basic rule of constructing color legends: order the categories in the way you expect readers to encounter them.
Here is the chart that I discussed the other day, with the data removed since they are not of concern in this post. (link)
First look at the pie chart. Like me, you probably looked at the orange or the yellow slice first, then we move clockwise around the pie.
Notice that the legend leads with the red square ("Getting It"), which is likely the last item you'll see on the chart.
This is the same chart with the legend re-ordered:
Simple charts can be made better if we follow basic rules of construction. When used frequently, these rules can be made silent. I cover rules for legends as well as many other rules in this Long Read article titled "The Unspoken Conventions of Data Visualization" (link).
I think the numbers do matter: in the original, the big worry was economy, followed by family, followed by getting it.
It follows that IF a pie chart had been the right choice (as you say, it so isn't), then the color choice should have been red for economy, orange for family, and yellow for getting it. THEN the pie should have started at twelve o'clock with the economy, and proceeded clockwise, AND the legend should have been red economy at the top and proceeding downward. These standard rules for pie charts help to minimise the effort needed to decode a pie chart, now we can be confident all pie charts operate alike. It's like having a standard layout in a cockpit, the better to safely fly the plane no matter which pilot takes the yoke.
(my employers once rolled out a corporate color scheme that did not contain a proper fire-engine red, and for kicks I tried to design alert reports without it. I found there is no substitute for a good fire-engine red: neither purple nor orange grab the attention the way it does.)
Sadly this whole discussion is made more difficult by the fact that colors, pies, and legends never should have been used in the above case. It should have been a horizontal bar chart with no colors and no legend.
Posted by: derek | Apr 04, 2020 at 04:08 AM
If you are going to use that chart type, then better not to use legends at all. Label the sectors, preferably in the same colours as the chart, and on a plain background.
Posted by: Meic Goodyear | Apr 06, 2020 at 09:25 AM