Maybe everybody already knows about this, but I couldn't find any mention of it in old threads. It's a mapping of British surnames.
I looked up my family's surnames on the site a couple years ago when it was a project of University College London. It has apparently been taken over by the National Trust since then.
http://www.nationaltrustnames.org.uk/What you do is click on "Surname Search" in the righthand corner of the little bar at the top of the page, and enter whatever name you want to look up.
You can find out what the UK geographical spread was of your name on maps from 1881 and 1998. You can find out the frequency and ethnicity. You can find out which social demographic classification has the most people with your name. You can find out where in Ireland, Australia, New Zealand, and the US, the most people with your last name moved.
I did it with my husband's surname and in 1881 there was only one tiny pocket of people in the whole UK. By 1998 they had spread out a bit, but not much! My grandmother's surname was in a slightly larger area in 1881, and quite widespread by 1998. The state in the US with the most people of my grandmother's surname was Iowa, which is where she was born! The social demographic classification (1998) for the largest group of people in the UK with my grandmother's surname was "Tower Block Living". Upon investigation I found that category was "Of all the types, these are amongst the poorest, in every sense..." What can I say?