The genius of Harry Beck’s (1902-74) design is its simplicity. By the 1930s London’s underground stretched in several directions on multiple lines serving stations miles into suburbia while also offering many stops close together in the city centre. The problem was how to fit it all on to one page – never mind a foldable map that commuters could carry and which would show a complex system in a way that could be easily understood.

Beck was an engineering draughtsman with London Underground who, in his spare time, mapped the system. He presented his map to his superiors in 1931 but they rejected it, coming back to him two years later suggesting a trial. He pared away all topographic details except the river Thames – this is not a map of London where you’ll find a picture of Big Ben or any extraneous above-ground information. He colour-coded the tube lines for instant recognition – with a key to that colour coding in a box – and ignored any attempt at realistic scale.

He solved the problem of indicating the complex idea of interchange stations – often in the most dense central areas of the map – with an open diamond shape. The trial was a success: commuters understood the map on sight, and Beck continued to modify it until 1960. His original design is still the basis for the map used by the London Underground now and its design principles influenced the maps for transport systems around the globe.