A really smart little project here by a couple of guys (names on the site), who have used publically avaliable data to map, ward by ward, the most common surnames. London Names therefore becomes a map of the most common ethnic communities in each area.
Its a really fascinating study, and well worth taking a look at, there are a few surprises in there.
There's also the equally smart World Names, which tracks surnames globally. Apparently my name is popular in Australia, North America and some of Western Europe. What a shocker.