Maps of bus, tram and trolley networks are, I think, more likely to use geographical maps of the city’s road network as their base layer than subway and rail maps. That’s not always the case—nor has it always been the case. Take this 1947 map of London’s trolleybus and tram routes, executed by Fred J. H. Elston. Cameron Booth finds that it has “more in common with modern best practices for transit diagrams than with something that’s now 70 years old.” On the other hand, Ollie O’Brien, writing at Mapping London, thinks that this map proves that “the simplicity of the tube map doesn’t translate very well to London’s complex road network. So perhaps this is why the idea almost didn’t survive for above-ground networks, and London’s more modern bus maps (now discontinued) have always used the actual geographical network.” Christopher Wyatt, sharing the map on Twitter, notes a big, Westminster-shaped hole in the trolley network that matches London’s speed limit map: “It does seem as though there is a historical pattern of aversion to transportation equity from Westminster.”