Pie charts considered harmful

“The only worse design than a pie chart is several of them, for then the viewer is asked to compare quantities in spatial disarray both within and between pieces.”

Edward Tufte, The Visual Display of Quantitative Information

Despite their high price tags, many enterprise security solutions display a lack of thought in their user interfaces. Around the Napera office, there’s a running joke about Steve Jobs alleged fanaticism on user interfaces at Apple and I’m known as somewhat of a curmudgeon on the topic. There’s a good reason for it, because I think user experience should be a design goal right up there with speeds and feeds.

A pet peeve of mine is reliance on pie charts. Circular shapes are generally an inferior way to display information, and research has shown that forcing users to compare data by angle is less accurate than using comparison by length. It is typically better to use a mechanism in which differences can be compared linearly.

A security product I used recently has a single pie chart front and center on their appliance dashboard. Because this chart delivers little useful information they’ve had to supplement it with a legend that is larger than the chart itself. Elsewhere in the interface they use linear charts, but they consistently fall back on pie charts for high level summaries. As someone in our office suggested, perhaps they do this because users expect to see pie charts, but it hurts the usability of the product.

Another network security product I used at a tradeshow last year has a Java based Command Center with significant UI challenges. It’s possible that large enterprise customers demand complexity in their user interface, and this product certainly delivers. The Command Center features a toolbar with a dozen generic icons that lack text labels until the user mouses over them individually. I’m not a huge fan of Microsoft’s Office 2007 redesign, but note how Microsoft label and group each of the icons on their new ‘ribbon’ so the user can quickly learn them without moving their mouse. No such luck for the network administrator it seems.

The Network Awareness dashboard in this same product features not one, but three pie charts, with detached labels that force you to mentally correlate the data to the chart if you wish to make sense of it (hence my Tufte quote above). The Real Time User Incidents screen has a red/green pie chart for Device Health, right next to a spacious table heading that would be a far superior way to display the same data. The rest of the dashboard features wireframe 3D bar charts that are scarcely more useful.

Colorblind users (up to 10% of men) would find much of the Command Center interface incomprehensible. Prominent use of red and green with no other visual cues is a major problem, combined with a lack of labels that might assist a colorblind user. Good user interface design avoids relying on color alone to express information, but adds cues such as shape or location. This not only helps color blind users, but also assists normally sighted people in quick and reliable interpretation.

You don’t need to study Tufte or have a degree in user interaction to see the problems with these interfaces. Stephen Few’s book Information Dashboard Design is barely two hundred pages and points out the major flaws with many so-called dashboards including those above.

Does the Napera product line have a flawless user interface? Like all software, it’s a work in progress. I am confident however that our first release is easier to understand than many enterprise security products that are in their third or fourth release.