There is an apocryphal story which every generation of Knowledge students hears. It relates an appearance (test) when a Knowledge boy tells the examiner that you could turn right into Farringdon Street from Holborn Viaduct.
The salutary lesson to be learned is that if he had just gone to that location he would have discovered there was a 60ft drop onto the road below.
[T]he hapless Knowledge boy had relied on his A-Z map and had learned the hard way that maps should not be slavishly followed. In fact deliberate errors called trap streets are included, and according to the BBC programme Map Man, broadcast in October 2005, its presenter Nicholas Crane, was told by John Frankel the managing director of Geographers’ who produce The Knowledge bible – the A-Z – that London alone has about 100 trap streets.
Apparently they are inserted to protect copyright. If a map is plagiarised the author can identify it as a copy of his own work. According to Peter Watts’ post in The Great Wen he has managed to clarify this reasoning.
The map itself cannot have a copyright as it is a representation of fact . . . the trap streets and deliberate mistakes change the work from being purely factual into a creative expression and thus able to be protected by copyright.
The example Watts gives is the ‘ski slope’ in the featured image above. There is no evidence of there ever having been a ski slope located in Haggerston Park.
Cartographers are naturally reluctant to disclose other ’deliberate’ errors. Some are known: Gnat’s Hill for Gants Hill; Bartlett Place (incidentally the name of Kieran Bartlett, an employee at Geographers’) for Broadway Walk E14; Moat Lane off Clandon Gardens N3 which doesn’t exist; Wagon Road EN4 which changes its name to Waggon Road after crossing a railway line, but left on the map with the single g spelling.
Another device map makers use to protect their copyright is that they will misrepresent the nature of a street in a fashion that can still be used to detect copyright violators but is less likely to interfere with navigation. For instance, a map might add nonexistent bends to a street, or depict a major street as a narrow lane, without changing its location or its connections to other streets.
Map makers have long had a cavalier attitude when it comes to the truth. Jonathan Swift wrote a poem in 1733 – and I paraphrase:
“If you’re a mapmaker and you don’t know what’s really out there you either make it up or you put in an elephant”.