Developers or designers of Fiori applications have frequently raised the question “Why Pie Charts are not in the Fiori Chart Library?”.
Indeed the SAP Fiori Chart Library does not contain any Pie Chart, and there is no plan to add it in a near future. The reason is that Pie Charts are not recommended for data visualization and can be advantageously replaced by simple bar charts.
This is a well-known issue and a lot of studies and articles exist on that topic:
- Save the Pie for Dessert (from Stephen Few)
- The Worst Chart In The World (from Walter Hickey)
- Chamber Of Horrors – Pies (HICHERT+PARTNER)
To make it (very) brief,
- Pie Charts does not work well with more than 5 categories
- It is difficult to compare areas (here slices)
- Sort is not immediately visible
- Small values cannot be read easily
- A legend is frequently needed
- Colors are needed just to distinguish slices
Pie charts are still frequently used mainly because this is how percentages are taught at school and also because a pie chart immediately conveys the idea of percentage. But that does not counterbalance all the weaknesses of this chart.
The links above give concrete examples of how to replace a pie chart by a chart bar chart or simple numbers.
If you have any use cases where you think a pie chart would be better, please do not hesitate to share.
This is a really interesting topic! I find it hopeful in a way that SAP is not offering the pie chart in order to ensure a higher level of usability for data visualization. That was probably not at all an easy decision to make. Good design is often about what to leave out.
It is really good to see that SAP is advocating good information visualization principles. Hopefully we won’t see 3D charts either.
If you’re more interested in this topic, I’d suggest reading Edward Tufte’s The Visual Display of Quantitative Information
“Above all else show the data”
Thank you for you good compilation of reasons against pie charts. I mostly agree with you and the reasons in the cited links.
Unfortunately, sometimes people ask for things that actually aren’t best for them. Pie charts are visually appealing but often used in cases where they are less helpful for grasping information precisely. It’s the same with PowerPoint-like dashboards that offer little information compared to rich information dashboards that are recommended and promoted by information visualization experts.
So, it is a kind of prioritization, which aspects you want to support more. An article that points out his aspect is e.g.: “Pie charts kill people” vs. “We want pie charts!”
Similarly color palettes can be optimized from the human perception perspective or from a marketing, branding or mood perspective.
Nevertheless there are a few use cases where a pie charts are more usable even for grasping accurate information. One of the most prominent ones is Harvey Balls in table cells or on maps for percentages: Harvey Balls are micro pie charts that contain exactly two slices and thus show exactly one percentage (and its remainder). They can be preferred to bars for the following reasons:
- They allow an easy estimation of the percentage compared to 100%, better than a bar (provided that you do not show a scale): Especially angles from the top position (i.e. 12 on the analog clock, likewise from 3, 6 and 9) can be estimated quite well. Parts that can be identified especially easily are: Full, half, third, quarter, sixth and eighth.
- Since the circumference of the pie is significantly longer than its width (more than three times), there is more “length” to differentiate and to show small values than on a bar.
- With a smaller width they allow slimmer table columns than single bar charts (unless you put the bar slim below or pale behind the related number) and lower table rows than single column charts.
Instead of listing and illustrating further use cases where pie charts outperform other chart types in information consumption, let me refer you to a web page that I have been sent just yesterday and that already describes my thought very well – and mentions even a few further aspects: Why Tufte is Flat-Out Wrong about Pie Charts.
In addition to these examples you can have:
- A pie chart with two most important segments among others: Here you let both start at the top, one clockwise and one counterclockwise.
- A pie chart with some important segments compared as a group to the rest: Here the important segments should be adjacent, with the first of them starting at the top. Typically these grouped segments have the same color and the other segment a deferent color, or they have similar colors that are clearly distinctive from the other segments colors.
- A pie chart with ordered segments: These are typically colored using a sequential color palette. Examples: Tasks with different due dates, issues of different severity
So, as you use bar charts for different purposes than line charts and therefore cannot generally say which one is better, you have the same with pie charts: Use them where they have their strengths (which might be more seldom than for bar or line charts) but not elsewhere.
I agree that pie charts do have their use cases and they may be good to visualize information when used to make the information more visually appealing. But strictly from information visualization point-of-view, when you have to convey information, I think that they are almost useless and can probably always be replaced with better visualization or no-visualization options.
Some comments on Kai’s post:
“maps for percentages”
I would say that a simple choropleth map with single hue progression with 4-6(8) different hues are superior. Pie charts on a map are really difficult to compare with each other and they usually also become so small that it becomes hard to measure the percentage value. With Choropleth map you define clear intervals that make it easy to see into which categories or percentage groups different map features belong to.
“let me refer you to a web page that I have been sent just yesterday and that already describes my thought very well – and mentions even a few further aspects Why Tufte is Flat-Out Wrong about Pie Charts:”
By going through the discussion in the link, it is quite clear that in most of the examples comparisons are done to equally bad visualizations (usually bar charts). Mostly going with raw numbers without any visualization would have been better.
“A pie chart with two most important segments among others: Here you let both start at the top, one clockwise and one counterclockwise.”
Why not use horizontal bar chart that is sorted by value? Or do you refer to something else than value by importance?
“A pie chart with some important segments compared as a group to the rest: Here the important segments should be adjacent, with the first of them starting at the top. Typically these grouped segments have the same color and the other segment a deferent color, or they have similar colors that are clearly distinctive from the other segments colors.”
I think stacked bar chart is usually better option in this case.
“A pie chart with ordered segments: These are typically colored using a sequential color palette. Examples: Tasks with different due dates, issues of different severity”
Horizontal bar chart would be better in this case also. It allows easier comparison of relative sizes of segments. If you look it from the user’s point-of-view, how can the user really know if the pie chart was ordered or not? With horizontal bar chart it becomes pretty clear.
In summary, I won’t say that pie charts are useless but in most cases you can definitely find a better option for visualization.
In my opinion SAP has found the perfect answer to this problem: a library like Analysis Path Framework allows the end user to switch the Chart type at runtime. And yes, sometimes I use a pie Chart – but for most uses cases not.
Hello dear contributors
The SAP Fiori Chart Library now contains a pie chart.
We have taken this decision for backward compatibility reasons. Indeed, some applications who decided to migrate to Fiori were using pie charts and that was not possible to replace the pie charts by bar charts for technical reasons. Mainly because all the charts were described in configuration files that customers carefully did create.
The other reason is that pie charts can be used in some cases, and I must confess I have been too extremist in this domain. As Kai Willenborg says, when we need to show the % of the first 2 or 3 slices, then a pie chart does the job better. Also when we need to show 2 slices only. Some guidelines will be written very soon on that topic.
Thank you all for your contributions
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