Topographical Transformation:
Harry Beck's London Underground Diagram

Consider the two diagrams below. The upper one is a reconstruction of a section of Harry Beck's well-known map (or diagram, if you prefer) of the London Underground system. The lower one shows the true spatial relationship between the lines and stations. Beck's diagram is easier to read, especially if you are planning a journey involving one or more changes between lines, but the "topographically transformed" data may mislead, for example when comparing the relative merits of taking the Tube versus walking or catching a bus.