If you're interested in the sources for the stats, check one of the replies above from 2007 - just email the artist and ask, I reckon.
@ Johnisfaster: of course the art would look similar for every country if it was done on a per capita basis; the artist's statement suggests he's interested in raising awareness of the sheer scale of it all, rather than a comment on efficiency.
Anyway, like I said - I just liked the pretty pictures!
