One city is far too unreliable. It could be a heavily gay city, like Brighton, or it could have very few gay people in. Nevertheless, the gene for homosexuality is naturally rare- if it weren't, procreation would be a very ineffient task indeed.
Definitely, but no one can know the exact percentage of the sexual orientation orientations, because as I said there are many closeted or "non-assuming" people, and it varies from one region,/city to another. But if you check on the net you'll find that the LGBT proportion is of almost 10% of the world, that's just to correct your estimate
