What I Learned Today

I am a latecomer, it seems, to some of Edward Tufte’s brilliant ideas. Today I stumbled across the sparkline, a “small, intense, simple dataword” (Tufte) that is best illustrated by example. Sparklines permit you to display a large volume of numeric information in a very tiny space, while conveying the information perhaps even more effectively than if you’d used a large floating figure or a table. Tufte posted a sparkline introduction, which is an excerpt from his book Beautiful Evidence. Many others have followed up with their own sparkline creations, sparkline generators (in perl, HTML, Excel, and even special font encodings), and sparkline critiques.

One tip I particularly liked had to do with aspect ratio; Tufte suggests (after William S. Cleveland, 1993) adjusting the vertical scale so that slopes are about 45 degrees (rather than very flat or very spiky). While this is simply a rule of thumb, to be violated if the situation calls for it, I did find his examples to be compelling; “lumpy” data does seem to be easier to visually process than “spiky” data.

But what really took my breath away was this particular example:

This is cited by Tufte as appearing in Robert Sedgewick’s 1998 “Algorithms in C”. It illustrates several passes of mergesort being applied to a 200-item list. It is absolutely brilliant! Whoever thought of visualizing the values (sort keys) as the angle of the lines was absolutely inspired. This graphic stole my attention as only a true work of art can. I’m still staring at it in fascination.

I’ll have to be on the lookout for places where sparklines could be the right solution in my next technical paper.