Most other subway maps in the world were actually based on Harry Beck's design classic of the London Underground map in the 1930's:
"Brilliantly, Beck compacted the sinuous curves, writhes and wriggles of a sprawling metro system that once snaked out, on single tracks, as far as Brill and its windmill in Buckinghamshire, and Ongar and its wooden Saxon church in Essex."
The reviewer, Jonathan Glancey, closes on a pensive note:
"Perhaps, though, London's map is ultimately a little sad. Its clear, logical, evergreen (and orange and yellow and silver and blue) design hides the fact that what appears to be a unified public service is being split apart to comply with barking (a stop on the District and Metropolitan lines) contemporary political dogma. But, then the map has always been a fiction of sorts. It remains, though, for all the faults it so brilliantly hides, and with all its global scions, an artwork for all to share, our mental map of London."