In 1933 Harry Beck drew a map of the London Underground.
It wasn't the first map of the London Underground, and it certainly wasn't the last, what marked it out was its simplicity, clarity and relevance to tube passengers.
Harry Beck wasn't a cartographer, he was an electrical draughtsman, which goes some way to explaining how he designed such a revolutionary map.
Rather than taking a map of London and drawing all of the tube lines across it, he treated it like an electric circuit design. To a large part he ignored distance, stations were positioned with respect to the tube lines that connected them, and not their geographical location.
By ignoring the real geographical layout of the tube map, he could arrange the lines and tube stations for clarity; when travelling from Baker Street to Holborn, you're interested in what lines to take and what changes to make, not the lay of the land.
Harry Beck's design is still used for the London Underground to this day, with slight modifications and the addition of new lines and stations, and it has been used as a template for train and tube maps throughout the world.
You can see the map at: