Tuesday, June 4, 2019

Concentric bubble charts are terrible; pie charts and moon charts may be OK

Robert Kosara writes about two recent papers on circular part-to-whole charts. I foresee there'll be a lot of discussion in the visualization world about this paragraph, which sounds sensible to me:
The visualization community may not like pie charts, but in the real world they’re hugely popular and very common. Rather than sneering at them (and the people who use them), why don’t we try to understand them better? In particular, the design space of part-to-whole charts is almost entirely unexplored. The only other chart that’s used for this purpose out in the world, the treemap, hasn’t been studied for this purpose much (if at all). And it seems to actually do worse than the pie chart (and the moon pie).
(Although I'd point out that stacked bar graphs are also used for that purpose.)

Two graphs from the papers (12), representing errors when estimating percentages by slice or segment, are particularly striking; if I had to describe them I'd say that pie charts and moon pie charts (Robert's term, although I propose 'eclipse charts') seem to be OK, but concentric bubble charts are terrible —this corroborates a hunch I've had for more than a decade,— and treemaps have their uses, but simple part-to-whole comparisons may not be one of them: