London tube maps

I often use images of the London tube map to explain what I mean by topological maps.  I have to confess I hadn't known much about the history of these maps, so was really glad to find this little treasure today, which shows the revolutionary influence of Harry Beck, who in 1933 proposed that much of the geographic information in the map -- information that he reasoned was not really necessary for people making transit decisions -- should be removed from the map, leaving something that looks more like a circuit diagram and is a familiar form for transit users the world over.  This type of map, as I discuss here, is a mirror of our mental spaces.