James Cheshire, of UCL's Centre for Advanced Spatial Analysis, has followed up on mapping life expectancy on tube lines  with a fun new map showing the top fifteen most common surnames in London by electoral ward .
Looking at the the most common surnames reveals the top-level trends to be roughly what you'd expect: overall, English names are the most common, with Indian and Bangladeshi names having sizeable hotspots (in northwest and northeast London for Indian names, and Tower Hamlets for Bangladeshi names). Welsh names are rather evenly spread throughout the capital, and Sikh, Jewish and Pakistani surnames each have their own focal points.
What's really fascinating is playing with the site's slider and comparing the most frequent surnames with the 10th or 11th most frequent. Some areas stay the same, but just move down the list of common surnames; so, for instance, Hounslow's most common name is Singh, and it's tenth most common name is Sidhu. Others have predictable ethnic mixes. Tower Hamlets, where the Bangladeshi surname Begum is the most common, breaks down to a mixture of Bangladeshi and Pakistani surnames when you get further down the list. And some, like Hammersmith and Fulham, reveal little pattern at all: scrolling through the list gets first English names, then Welsh, then Scottish, Pakistani, Irish and "other".