Charting: not as easy as pie

SEED magazine's recent rundown of the pluses and minuses of charting is well worth a read, especially if you haven't spent hours and hours considering which graphical formats are most effective and why. To wit:

Many psychoperceptual studies have explored the human mind’s aptitude for gleaning information from pictures. Unfortunately, the pie chart incorporates tasks that we humans systematically fail to perform accurately, all those exercises that come at the bottom of the hierarchy of perceptual tasks... So although we’re good at comparing linear distances along a scale — judging which of two lines is longer, a task used in bar graphs — and we’re even better at judging the position of points along a scale, pie charts don’t bring those skills to bear. They do ask us compare angles, but we tend to underestimate acute angles, overestimate obtuse angles, and take horizontally bisected angles as much larger than their vertical counterparts. The problems worsen when we’re asked to judge area and volume: Regular as clockwork, we overestimate the size of smaller objects and underestimate the size of larger ones, to a much greater degree with volume than with area.

Again, as with so many aspects of life (!), infoviz is at its heart not about making the hard info just look pretty — it's a means of communication, and if readers can't decipher something you've rendered, they are not receiving your message.

"Getting Past the Pie Chart" -- SEED