The Centre for Metropolitan History and Museum of London Archaeology wanted a map that could help them visualise data from the 18th and 19th centuries.
They started by taking John Rocque’s 1746 map of London, putting the 24 parts together, then georeferencing it.
(For non-cartographers, georeferencing is "the process by which an electronic image of the earth is located on to the earth in the right place, so that the features it depicts overlie the same features shown on a current measured reality".)
The results were overlaid onto a Google map, and voila!
You can travel through London as it was in 1746, and, as a added bonus, see the differences between then and now by moving the StreetView icon around.
Example: in 1746, Southwark was mainly a giant field, but look at all the blue lines on top of it! They’re modern roads, and the bottom right corner of St George’s Fields is now Elephant & Castle roundabout.
The map is incredibly detailed — you can zoom in anywhere — and there are dozens of boats on the Thames, which is nice. This is London Bridge:
There’s a lot more geeky map fun to be had on the Locating London website, including another map from 1869-1880, and there’s tons of data about all the different areas from the18th and 19th centuries.