In an article that attempts to define and explain information design and information designers, Terry Irwin, design consultant, educator and founder of MetaDesign in San Francisco writes:
“Information Designers are very special people who must muster all of the skills and talents of a designer, combine it with the rigor and problem solving ability of a scientist or mathematician and bring the curiosity, research skills and doggedness of a scholar to their work.”
To honour these often-unsung heroes, we’re doing a piece on information design. From the do’s and the don’ts to the nit-picky things in between, here we have the elusive pie chart.
Where did they come from?
Well, the invention of pie charts is generally credited to William Playfair, a Scottish engineer and political economist. Playfair is a key figure to the history of quantitative graphics as he is also said to have invented line graphs and bar charts. And, in case you’re wondering what a pie chart is, the technical definition is: a circular chart divided into sectors that illustrate proportion based on percentages.
When to use a pie chart?
As an information designer, it’s important to remember that with great power comes great responsibility. When given data you have to ask yourself ‘What is the most important point to be made?’
“Consider the information first and the ‘look of it’ later,” says Nigel Holmes of Impress Magazine.
When communicating data it is very easy to skew the information when you get carried away with the visual aspects of it. Stay true to the data and its purpose and your graphs will rarely go astray.
“The pie chart is a simple information graphic whose principal purpose is to show the relationship of a part to the whole. It is, by and large, the wrong choice as an exploratory device, and it is certainly not the correct choice when the graph maker or graph reader has a complicated purpose in mind,” (Ian Spence, No Humble Pie: The Origins and Usage of a Statistical Chart).
More complicated than it looks, the pie chart is often misused by people who believe they can make the poor circle do more than it was designed for. The best way to determine whether or not to use a pie chart is to think about your data.
- Are there significant visual differences in values?
- Will it be easy to get a quick snapshot of your data?
- Is your main goal to show a comparison of data within one chart?
- Are your quantitative values independent of change in data over time?
If you answered yes to all of those questions, then the pie chart might just be the right choice for you. The pros and cons chart below outlines the plus and minus points to using a pie chart and might also help you to determine whether or not to go down the path of the pie.
Easy as pie you say? Well, you have to remember that if exact values are important to telling the story of the data, then you might as well just go with a table. When you have too much data on a pie chart or if your graphs are too small, the slices become pretty hard to read – especially as you get closer to the centre of the circle. Of course, if you’re Edward Tufte, then you would avoid pie charts like the plague. In his book, The Visual Display of Quantitative Information, he states,
“A table is nearly always better than a dumb pie chart; the only worse design than a pie chart is several of them, for then the viewer is asked to compare quantities located in spatial disarray both within and between charts… Given their low density and failure to order numbers along a visual dimension, pie charts should never be used.”
Alternatives to Using a Pie Chart
Using the data from AdMob’s Tablet Survey on the average time spent using tablets we’ve come up with a few different graphic variations to explore the options around what to use instead of a pie chart.
1) Open-centre pie chart
- Removing the center eliminates the trap of trying to read the chart from the inside out.
- The center should never be used to hold the title or legend of the chart — remember to keep things simple and uncluttered.
- Key Benefit: showing the relationship between findings and comparing proportions.
2) Progress Bar:
- Depending on the data, this kind of chart can be used quite effectively instead of a circle graph.
- Like pie charts though, these work well only if there are significant differences between data values.
- These kinds of charts lose all meaning when you have multiple charts and try to compare them to each other — think “quick snapshot”
- Key Benefit: rather than calling out specific values, this method emphasizes the the variable factor (in this case, how much time in hours was spent on the device)
3) Bar chart:
- Clean and easy to read as long as the variables on the x and y axes are clear.
- This is arguably more clear and easier to read at a glance than a pie chart.
- Key Benefit: easier to read the difference between data findings (the variation of the heights of the bars)
- Using some subtle colour variations and very clear typography, you can’t go wrong with tables
- Readers may spend a tiny bit more time with these than with graphs but what they read from it will be accurate every time
- Key Benefit: easy to compare specific numerical values and qualitative data
So, if the client says “Just put it in a pie-chart,” you’re now armed with evidence about why a pie chart may or may not be the best choice for your data set. With that in mind, we hope that you are now better equipped to tackle your next big data visualization project!
Stay tuned for more about information design and let us know what your thoughts are. Feel free to leave us a comment, we’d love to hear from you!