26 November 2009: Tube maps have been part of London life since the birth of the Underground, and were initially as confusing as the city itself: a tangle of different lines woven around the curving River Thames. Enter Harry Beck, an LU engineer who in 1931 came up with the radical idea of presenting the ever-expanding network as a circuit diagram rather than a geographical map – so creating a modernist design icon that has never been bettered. But as the Oystercard zone expands, are its days numbered? Take a look back at the changing face of the tube over the last century