Thursday, May 26, 2011

Optical Disillusion

I dislike chartjunk. Not only is there a trend toward the incomprehensible but the movement comes with a ridiculous amount of flair. For all I can tell there exists a competition between infographic creators where the rules are based solely on who can cram more slop on a page.

Besides my obvious distaste for the style, there are sacrifices being made that compromise, or even forgo, the actual message - often without awareness or malice. Take, for example, the evolution of the pie chart.

For the sake of this example lets ignore the fact that a pie chart is a particularly poor way to display data to begin with. As a measure of two variables it provides a rough estimate of dominance but beyond that the human eye can not distinguish relative quantities across the various shapes. In almost all cases a simple bar chart provides a more precise description - even in the two variable case. A visual display of data should be able to stand on its own without the need of labels describing quantities or values. The pie chart fails in this respect, but I digress.

Consider a simple pie chart of two variables.
  (As a measure of the strength of a pie chart as a communication tool, can you guess the values of the two areas? Go ahead, take a guess.)

The red portion of the chart is 55% and the blue portion is the remaining 45%. Without labels it is hard to distinguish exactly but serves to at least show the dominance of red over blue. The problem with trendy infographincs is that a simple pie chart is almost never sufficient in the layout. It needs exploding, or gradients, or even a third dimension.

Lets dress it up a bit and make a 3D pie chart with the same values.
So what's my beef about that? Lets consider the new representative areas of the chart. In the first chart, the values were inconspicuous but at least the color representation mapped directly to the underlying data.

Standard Pie Chart (red pixels) : 44295 (55.000%)
Standard Pie Chart (blue pixels): 36188 (44.900%)

In this new 'cooler' version of the chart we have skewed the data representation and thus our understanding of the overall message. In fact, by visible surface area alone we have changed the meaning of the chart entirely!

3D Pie Chart (red pixels) : 44792 (47.300%)
3D Pie Chart (blue pixels): 49740 (52.600%)

What is now required of us in this new chart, along with somehow mapping area to value, is to do accurate mathematical transformations in our heads to convert the 3D surface to an area in 2D. In fact, we need to now be able to deduce that roughly 52% of viewable surface area translates to 45% underlying data. The skew depends on the pitch, yaw, and roll so there is no magical formula here - every view will be a different mapping between surfaces.

I don't think people consider these details when compiling charts. In my estimate they are only trying to provide the most 'eye candy' for the intended consumer. The behavior is facilitated by common built-in chart generators (only 48 out of Excel's 288 pie chart variations are simple 2D charts) but there is no warning about the possible loss of meaning.

I'm certainly not among those pushing the envelope with infographics - this definitely makes my opinion biased. I keep things as simple as possible and for most data hungry crowds my approach is just too boring against current standards. I do believe there is a middle-ground, however; a place where rich graphics convey accurate data with minimal annotation markup. I only wish I knew how to bridge the gap.

A huge thanks to Dana Brown for taking the time to review and provide feedback on the first draft of this post.

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