Check out these maps I found on the internets!
Aside from the problem of purple standing out way more than orange yet actually representing a lower figure, these maps don’t account for population; they’re only looking at raw numbers. So there appear to be major concentrations of Buddhists around Tokyo, Nagoya, Osaka, and Fukuoka. But those are just the largest cities in Japan, so these maps tell us nothing.
Or really, I can just let XKCD explain:
Rollover text: “There are also a lot of global versions of this map showing traffic to English-language websites which are indistinguishable from maps of the location of internet users who are native English speakers.”