challenges with double donuts
Recently, I’ve gotten a couple of questions about donut charts: Are donuts a good alternative to pies? When would you use a donut chart? Food-wise, I’d be happy for either a pie or a donut—both are great! However, graph-wise, I find both can be challenging. We’ve posted about pie charts before and explored some alternatives to pies. A donut chart is a cousin to the pie chart—it's essentially a pie chart with a circle cutout in the center. It turns out that the same limitations of pies also apply to donut charts.
Let’s consider the real-world example below.
Here we have not one, but two donuts! It takes a while to figure out what this data represents. Based on the title, it appears that we’re meant to compare the categories of the donuts across the two charts. With the sections in different places, this is rather challenging.
One may argue that the colors and donut form make the data more visually interesting; however, this often hinders our ability to understand the data. Let’s look at some strategies to make this information easier to comprehend.
Order data in a thoughtful and intuitive way
Starting at the top of the donuts and working clockwise around, the categories are arranged in alphabetical order. This order works well if someone is looking for a specific category and wants to quickly look it up in the list (particularly a long one). In this case, however, it may be more interesting to quickly scan to see the highest and lowest project risk categories. By plotting the values in both graphs in order from most to least Issues Raised, we can make this task simpler for our audience.
Now we can see the Supplier, Schedule, and Budget categories are the top three in Issues Raised. We can also start to see some differences between the two visuals. For example, Supplier is not the top category for Issues Resolved in the right graph.
Put things you want to compare close together
Having physical distance between things makes comparing them more difficult. Other chart types, like bar graphs or slopegraphs, would allow us to put the categories next to each other for an easy visual comparison. Since the Issues Resolved are a subset of the total Issues Raised, I’ll opt for a stacked bar chart using absolute values, instead of percentages.
Having the information on a common axis now makes the task of comparing the categories and the status of the issues much easier.
Apply colors sparingly and use words wisely to make the takeaway clear
Using stacked bars with just two categories—Resolved and Unresolved—also helps to reduce the number of colors that were in the original donut charts. Rather than applying color for decoration or interest, or to make multiple categorical distinctions, we should use color sparingly and strategically to draw our audience’s attention to what we want them to see. We can also make the point of the visual clear by writing out the takeaway and including it next to the data. This helps people know where to look for the evidence of what you're telling them.
Check out the impact of simplifying the original view to make less work for our audience to understand and see the main takeaway.
Note that there is a time and place for donuts (and pies!)—see our related challenge for some ideas if you are considering one of these circular-shaped charts.
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