All I’m going to do this week I point you to Andy Kirk’s blog. He’s considering bivariate choropleth maps. You what? Each region has two variables. Maybe one gets encoded as hue and the other saturation. No way. Yes way, and it’s not necessarily the train wreck you’d imagine. Check them out.
Of course, by superimposing objects rather than colouring in (because colour is, you know, so beguiling as a visual parameter to mess around with, yet so poorly perceived), people have been doing this for ages. Bertin’s much-quoted and less-read book has many such examples, which mostly fall flat in my view. As he wrote: “It is the designer’s duty … to flirt with ambiguity without succumbing to it”. Bof!