The Tube map is a schematic transit map representing the lines and stations of London's rapid transit railway systems, namely the London Underground (commonly known as the Tube, hence the name), the Docklands Light Railway, London Overground and the Emirates Air Line aerial tram. As a schematic diagram it shows not necessarily the geographic but rather the relative positions of stations along the lines, stations' connective relations with each other and fare zones. The basic design concepts have been widely adopted for other network maps around the world, especially that of mapping topologically rather than geographically. What is now a single network of lines controlled by a single organisation began as a collection of independent underground railway companies that constructed lines in the 19th and early 20th centuries. These companies published route maps of their own services but did not, generally, co-operate in advertising their services collectively.
Contributions by DanielRigal, Musicandcomedy, and A is to B as B is to C.