Aug 112016
 

Overview

As readers of this blog know, I have my problems with donut charts.

That said, I acknowledge that they can be cool and, under certain circumstances, enormously useful.

On a recent flight I was struck by how much I liked the animated “estimated time to arrival” donut chart that appeared on my personal TV screen. An example of such a chart is shown in Figure 1.

Figure 1 -- Donut chart showing progress towards completion of a flight.

Figure 1 — Donut chart showing progress towards completion of a flight.

I find this image very attractive and very easy to understand — I can see that I’m almost three-quarters of the way to my destination and that there are only 49 minutes left to the flight.

So, given how clear and cool this is, why not use them on a dashboard?  And if one is good, why not use lots of them?

It’s the “more than one” situation that may lead to problems.

Trying to make comparisons with donut charts

The flight status chart works because it shows only one thing only: a single item’s progress towards a goal.

Let’s see what happens when we want to compare more than one item.

Consider the chart in Figure 2 that shows the placement rates for Fremontia Academy.

Figure 2 -- Donut chart showing placement percentage.

Figure 2 — Donut chart showing placement percentage.

A 95% placement percentage is really impressive.  Is that better than other institutions?  If so, how much better is it?

Figure 3 shows a comparison among three different institutions using three different donut charts.

03_3Donuts

Figure 3  — Three donut charts displaying placement percentages for three different institutions.

Before digging deeper let’s replace the three separate donuts with a donut-within-a-donut-within-a donut chart (Figure 4.)

Figure 4  -- A concentric donut chart (also called a “radial bar chart” or a “pie gauge.”)

Figure 4  — A concentric donut chart (also called a “radial bar chart” or a “pie gauge.”)

“What’s the problem?” you may ask, “these comparisons are easy.”

While you may be able to make the comparisons you are in fact working consierably harder than you need to be.

Really.  Let me prove it to you.

Let’s suppose you wanted to compare the heights of three famous buildings: One World Trade Center, The Empire State Building, and The Chrysler Building (Figure 5).

Figure 5  -- Comparing the size (in feet) of three large buildings.

Figure 5  — Comparing the size (in feet) of three large buildings.

Now that’s an easy comparison. With virtually no effort we can see that One World Trade Center (blue) is almost twice as tall as The Chrysler Building (red).

Now let’s see how easy the comparison is with donuts (Figure 6.)

Figure 6  -- Three large buildings twisted into semi-circles.

Figure 6  — Three large buildings twisted into semi-circles.

Here are the same buildings rendered using a concentric donut chart (Figure 7).

Figure 7  -- Three skyscrapers spooning.

Figure 7  — Three skyscrapers spooning.

Yikes.

So, with this somewhat contrived but hopefully memorable  example we took something that was simple to compare (the silhouettes of buildings) and contorted them into difficult-to-compare semi-circles.

With this in mind, let’s revisit the Placement example we saw in Figure 3.

Here is the same data rendered using a bar chart.

Figure 8 -- Placement percentage comparison using a bar chart.

Figure 8 — Placement percentage comparison using a bar chart.

The comparison is much easier with the bars than with the donuts / semi-circles. You can tell with practically no effort that the blue bar is approximately twice as long as the red bar, even without looking at the numbers.

Indeed, that’s a really good test of how clear your visualization is: can you compare magnitude if the numbers are hidden?

Pop quiz — how much larger is the orange segment compared to the red segment?

Figure 9 -- Trying to compare the length of donut segments is difficult.

Figure 9 — Trying to compare the length of donut segments is difficult.

Now try to answer the same question with a “boring” bar chart.

Figure 10 -- Comparing the length of bars is easy.

Figure 10 — Comparing the length of bars is easy.

With the circle segments you are squinting and guessing while with the bars you know immediately: the orange bar is twice as large as the red bar.

More downsides for donuts

In addition to comparisons being difficult, how would you handle a situation where you exceeded a goal?  For example, how do you show a salesperson beating his / her quota?  With a bar chart you can show the bar going beyond the goal line (Figure 11).

Figure 11 -- With a bar chart it's easy to show more than 100% of goal.

Figure 11 — With a bar chart it’s easy to show more than 100% of goal.

How do you show this with a donut chart?

Rhetorical question.  You can’t.

Conclusion

If you only have to show progress towards a single goal and don’t need to make a comparison then it’s fine to use a donut chart. If you need anything more complex you should use a bar chart as it will be much easier for you and your users to understand the data.

Special thanks to Eric Kim for creating the building images.

 

Jun 222016
 

Overview

My obsession with finding the best way to visualize data will often infiltrate my dreams. In my slumbers I find myself dragging Tableau pills in an ongoing pursuit to come up with the ideal dashboard that shines light on whatever data set has invaded my psyche.

But is the pursuit of the perfect dashboard folly?

Probably, as I’ll explain in a minute, but I don’t want to suggest anyone not at least try for the clearest, most insightful and most enlightening way to display information.

Is this way is the best way?

This pursuit of the ideal chart preoccupies a lot of people in the data visualization community. Consider this open discussion between Stephen Few and Cole Nussbaumer Knafflic that transpired earlier this year.

As you will read, Few weighs in on Knaflic’s book Storytelling with Data and her use of 100% stacked bar charts.  He cited this particular example.

Figure 1 -- Knafflic's 100% stacked bar

Figure 1 — Knafflic’s 100% stacked bar

Few argued that there was a better approach and that would be to have a line chart with a separate line for each goal state.

Figure 2 -- Few's line chart

Figure 2 — Few’s line chart

Having written about visualizing sentiment and proclivities, I chimed in suggesting that a divergent stacked bar chart would be better (see Figure 3.) I think this presents a clearer and more flexible approach, especially if you have more than three categories to compare as the 100% stacked bar chart and line chart can become difficult to read.

Figure 3 -- My divergent stacked bar chart

Figure 3 — My divergent stacked bar chart

The ongoing public discussion was engaging and congenial but I’ve seen similar cases where one or more of the parties advocating a solution become so certain that his / her approach is without a shadow of a doubt the only right way to present the data that tempers flare high. Indeed, I’ve seen instances where some well-respected authors have declared a type of “Sharia Law” of data visualization and have banned so-called heretics and dilettantes from leaving comments on blogs and even following on Twitter!

My take? While I prefer the divergent stacked bar, the real question is whether the intended audience can see and understand the data. In this case, if management cannot tell from any of the three charts that there was a problem that started in Q3 2014 and continued for each quarter, then that company has some serious issues.

In other words, if the people that need to “get” it can in fact make comparisons, see what is important, and make good decisions on their new-found understanding of the data  — all without having to work unnecessarily hard to decode the chart — then you have succeeded.

I’m not saying don’t strive to be as efficient , clear, and engaging as possible, it’s just that the goal shouldn’t be to make the perfect chart; it should be to inform and enlighten.

And in this case I think all three approaches will more than suffice.  So stop arguing.

Understanding and educating your audience

Earlier this year I got a big kick out of something that Alberto Cairo retweeted:

Figure 4 -- Avoid Xenographphobia: The fear of unusual graphics / foreign chart types.

Figure 4 — Avoid Xenographphobia: The fear of unusual graphics / foreign chart types.

Xenographphobia! What a wonderful neologism meaning “fear of unusual graphics.”

So, why do I bring this up? While it’s critical to know your audience and not overwhelm them with unnecessary complexity, you should not be afraid to educate them as well. I’ve heard far too often people proclaim “oh, our executive team will never understand that chart.”

Really? Is the chart so complex or the executive so close-minded that they won’t invest a little bit of time getting up to speed with an approach that may be new, but very worthwhile?

I remember the first time I saw a bullet chart (a Stephen Few creation) and thought “what is this nonsense?”  It turns out it wasn’t, and isn’t, nonsense.  It took all of 60 seconds for somebody to explain how the chart worked and I immediately saw how valuable it was.

Figure 5 -- A bullet chart, explained.

Figure 5 — A bullet chart, explained.

I had a similar reaction when I first heard about jump plots from Tom VanBuskirk and Chris DeMartini. My thoughts at the time were “oooh… curvy lines.  I love curvy lines! But I suspect this is a case where the chart is too much decoration and not enough information. I bet there are better, simpler ways to present the data.”

Figure 6 -- Jump plot example. Yes, these are very decorative, but they are also wickedly informative.

Figure 6 — Jump plot example. Yes, these are very decorative, but they are also wickedly informative.

Then I spent some time looking into the use cases and came to the conclusion that for those particular situations jump plots and jump lines worked really well.

That said, there are some novel charts that I don’t think I will ever endorse, with the pie gauge being at the top of my list.

Figure 7 -- The pie gauge, aka, a donut chart within a donut chart, aka, stacked donut chart. I won't go into the use case here but a bullet chart is a much better choice.

Figure 7 — The pie gauge, aka, a donut chart within a donut chart, aka, stacked donut chart. I won’t go into the use case here but a bullet chart is a much better choice.

So, what should we do?

I’ve argued that you should always try to make it as easy as possible for people to understand the data but you should not go crazy trying to make the “perfect dashboard.”

I also argue that that while you should understand the skillset and mindset of your audience, you should not be afraid to educate them on new chart types, especially if it’s a “learn once, use over and over” type of situation.

But what about aesthetics, engagement, and interactivity? What roles do these play?  Is there a set of guidelines or framework we should follow in crafting visualizations?

Alberto Cairo, in his book The Truthful Art, suggests such a framework based on five key qualities.

I plan to write about these qualities (and the book) soon.