Comment 2 for bug 851424

The genre mapping appears to be as follows at the moment:

blues --> blues
classic --> classic, classical
country --> country
disco --> disco
funk --> funk
rock --> rock, heavy, hard
metal --> metal, heavy
hip hop --> hip-hop
house --> house, chillout, minimal, hard, electronic
new wave --> new-wave
r-and-b --> r-and-b
punk --> punk, punk rock, hardcore, heavy
jazz --> jazz
pop --> pop
reggae --> reggae
soul --> soul, gospel
techno --> techno, minimal, trance, chillout, electronic, electronica
other --> other, african, alternative, ambient, asian, brazilian

Having glanced through my own music collection, I have the following genres present which aren't represented: Folk, Traditional, Dance, World, Ambient, Oldies, Heavy Metal, Christmas, Latin, Celtic, Soundtrack, R&B, Rap, Rap & Hip Hop, Rock and Roll, Opera
There are bound to be others (all the many, many varieties of metal, for example) that I'm missing. Many of these fit fairly nicely with the existing genre filters, so the mapping could be easily extended to add more genres in without having to add any more filter options to the lens. The genre mapping is defined in http://bazaar.launchpad.net/~unity-team/unity-lens-music/trunk/view/head:/src/genre.vala