The World’s 15 Most Complex Subway Maps

For all its colorful frenzied glory, the Tokyo Metro map isn’t the most complex subway guide in the world. New York and Paris both have it topped—at least in the eyes of one group of theoretical physicists and mathematicians.

Researchers Riccardo Gallotti and Marc Barthelemy of the CEA-Saclay in France and Mason Porter of the University of Oxford in the U.K. recently set out to calculate the maximium transit map information someone can “reasonably process.” The goal, they write in Science Advances, was to see whether the growth of urban transportation systems has led to visual guides that “exceed our cognitive limits.” If that’s the case, then city residents and visitors might soon have to rely on digital navigation apps less as a crutch than as a necessity.