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A focus on visualizations: Pie charts

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Sweetspot pie chart

In the world of reporting, there is an anti-pie fever going around. Why you ask? Simple: humans have a difficult time judging size by relative area rather than length. By relying on the visual interpretation of size, the pie chart often delivers a poor user experience by making it difficult to interpret information, which could be detrimental to discovering insights.

While the pie chart is likely the most familiar visualization (as it is used excessively in news stories, blogs, etc.), it is best used to give a general idea of how data compares as parts to a whole rather than to try to assign specific values to different categories. This is fine when you’re comparing data categories with large differences between their values, but it may not be the best visualization to represent critical data to your stakeholders.

When to use a pie chart When NOT to use a pie chart
Pie charts are best used to represent:

  • parts of a whole
  • mutually exclusive variables (no overlapping data)
Pie charts should not be used when:

  • The parts do not add up to a meaningful whole
  • searching for a trend

How to read a Pie Chart?

Well, this is the big issue because it’s not “as easy as pie”… It is simple to understand when there are considerably larger slices or perfect 90/180 degree angles. However, we can’t actually deduce the exact value of each pie slice otherwise.

Pie Chart bar graph alternative

The pie and column chart above both show the exact same data. Which one do you find easier to read? The column chart is just as capable, if not better, at giving an accurate representation as to how each variable compares, plus it also gives a precise measurement for each. The only thing that the pie chart does, however, is compare the variables as parts of a whole. Although this may not be a built-in feature, column charts are also capable of showing parts to whole relationships, which they do by displaying percentages. Keep this in mind when deciding which chart best represents your data.

Parts to a whole:

We’ve already mentioned that the purpose of a pie chart is to show meaningful parts of a whole. This signifies that any graph displaying a cumulitive sum of, say, 193% would not only be showing inaccurate information, but would totally miss the mark of when and how to use a pie chart. You may recognize the infamous Fox News chart which did just that!

fox news pie chart

You can never have too much pie, or can you…?

You wouldn’t want to overslicedpiechartcut a real pie into tiny, worthless pieces, so why do it in your reports? Respect your readers by presenting them with only enough variables to give them a general overview of what is occurring, rather than trying to overwhelm them with information. Otherwise you will end up with an overly complicated, extremely colorful and uninterpretable mess.

One way to overcome this situation is by limiting how many factors you demonstrate. You may choose to represent your top 5, and then merge the other, smaller categories into their own pie slice, labeled “other”.

Legend & Labels

Pie Chart LegendYou don’t want to waste your reader’s time. In order to assist them in interpreting your graph accurately, quickly, and effectively, label variables in a way that allows readers to gather the information they need with ease.

Legends are always an option, but we find that oftentimes readers are distracted by bouncing back and forth between pie charts and their legends. The situation can easily get more complex when you add in the color factor. Shades of the same color just continue to complicate an already confusing situation.

piechartdirectlylabeled

At Sweetspot we find that the easiest, most effective means of labeling pie charts is to simply ditch the legend and label the variables directly. We suggest, however, that whilst employing this approach that you do not over-slice your graph. The more variables you have, the more confounding your graph will become. You may also consider including the numerical value or percentage associated with each variable to provide further insight.interactive pie chart

 

Interactive elements may also aid end users in successfully interpreting the metrics you’d like to report. In the accompanying graph, the reader can easily see that they are receiving more exposure from offline media sources, but we cannot simply discount other factors because they are relatively less significant. In order to facilitate the interpretation of variables, Sweetspot demonstrates exact values when you scroll over a section of a chart.

 

3D Pie Charts:

How can you make an already difficult graph just that much harder to interpret? Make it three dimensional. Without hesitation, we suggest completely avoiding this option.

3D Pie Chart

Donuts anyone?

Donut ChartMaybe it is meant to be aesthetically appealing, but cutting out the center of a pie chart to make a donut chart simply has an adverse effect by taking away the central point of reference that helps us view the angles of each slice. After all, the most effective way of interpreting a pie chart is by studying the angles of the sections at the point where all the lines intersect. Before you resort to using a donut chart, try visualizing your data with a normal pie chart, labeled directly.

Conclusion:

In the famous words of Stephen Few, “save the pies for dessert”. Surprising as it may be to all those pie lovers out there, this visualization is not always the best choice as it has very little value other than for representing a parts to whole relationship. Carefully consider how well a pie chart can reflect your metrics compared to a bar graph when deciding on the best way to measure your marketing efforts! You may find the pie chart just doesn’t cut it.

Please share your stories with us! When has a pie chart allowed you to effectively communicate your data to stakeholders?

 

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Holly McKendry

Sweetspot Marketing Director. Wakeboarder & travel enthusiast. Communication Studies graduate of Texas State University, San Marcos.


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Tim Waring

Great Blog Holly!

Published on , 11:12 am   

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