The "map" is more than adequate for providing an introduction to the various genres of metal with a fun interface, but it couldn't possibly be comprehensive. (@ Ron P., I seriously doubt there's no Iron Maiden anywhere; perhaps you didn't sample all the genres?)
---------- Post added at 06:22 PM ---------- Previous post was at 06:21 PM ----------
Yep, under New Wave of British Heavy Metal there are loads of Iron Maiden songs.
Anyway, it's a fun app. Thanks for sharing the link.