LONDON’S underground rail map has been an inspiration to topologists ever since Harry Beck produced . Before then, travellers had to grapple with representations of the of the city linked by a confusing network of tunnels dug by competing companies. Beck tidied it all up by showing the various lines as, well, lines, emphasising their connectedness rather than their geography.
In December 2009, Transport for London (TfL) took the topological theme a step further. It had had problems with the Circle line, one of which was a fashion among some…
