[ImNotJohn] For years I lived in a street that the local "A-Z" type guide showed as having a cross street where there wasn't so much as a kerbstone. When this error survived two reprintings I got clued in. By pure chance I was living next door to a copyright protection scheme. The map publisher had put in a fake street so that they could easily catch competitors who saved the cost of a survey just by copying their maps. I've learned since then that an awful lot of this sort of thing goes on. Dictionaries, thesauri (?) and encyclopediae (??) have fake entries in them to snare copyright infringers. The original pubishers work on the theory that you'd be unlikely to actually read the articles/entries since you can't get to them in any day-to-day use of the dictionary/thesarus/encyclopedia but only by reading through them serially.
I have to admit, sending someone off a cliff seems a bit much though. I hope this gets fixed in GPS sets since judging from recent news items some GPSers are a bit too slavish when it comes to following the directions their boxes give them and I wouldn't be surprised to read of someone stepping out into empty space.
I have a couple of 1:25000 maps covering my area of residence. A month or so ago I dug out one of them in order to scan part of it and send the resultant image to a cyber-acquaintance. I doubt that I had referred to this publication within the last three or four years. I also forgot to put it back in stowage that evening. The following afternoon my wife came home and plonked down before me a new copy of the very same map. Having given her a puzzled look she explained that the previous evening she had looked for the 'missing' map and, not finding it, thought it best to buy a new one.