The British Library has an exhibit happening right now of maps that changed the world. The Daily Mail has a smashing top-ten. Above is the first map of the London Tube system, from 1933:
Dismissed as too ‘revolutionary’ when it was first submitted in 1931, Harry Beck’s Underground map solved the problem of how to represent clearly and elegantly a dense, complex interweaving of train lines.
Placing the stations at similar intervals regardless of their true locations amplifies the area of central London, increasing its clarity, while the straight lines and interchange symbols confer a simplicity and order on the network. A cartographic icon.
Ten of the Greatest Maps That Changed the World [DailyMail]