First of all, it's not GPS.
GPS is, as we know, a Global Positioning System. *ALL* it does, and all it can do, is say You are probably here.
The problem is the car's nav system, not GPS.
The nav system requires roads--it freaks out a little or a lot if you try to go offroad. Anyone who's traveled on a brand new road has probably had fun watching the car's nav system eagerly but desperately try to reconcile the GPS's location against the non-route. It usually (in my car's case) tries to locate my car on any vaguely nearby road... and then, as I keep driving, jumps me to the next road... then the next... until it finally gives off some sort of digital sigh and just says UNKNOWN ROAD.
There are two stories in this thread that illustrate this.
First, the guy's NOT going to find an off-road fishing hole unless his car's software knows about it. Not surprisingly, programmers of car nav systems don't spend a whole lot of time worrying about watering holes unless there's a road right there or it can be used as a landmark. 90% of lakes, creeks, and streams (at least) don't even appear on a nav system. The guy didn't know the difference. The car's nav system gets him to the nearest intersection... but then a map should be used next. See Dougo83's comment. I agree.
Second, the ridiculous things Mapquest and other map tools use are just as guilty. Most of these systems are not terribly reliable. Mapquest in general is so bad I went to Yahoo! maps for about two years. Then, programming bugs there drove me nuts so badly that I went to Google maps... so far, it hasn't screwed me up. It will one day, but I haven't seen it yet.
The nav system and the map software share the exact same problem: bad data, without an easy way for folks to recognize or compensate for it. That non-existent right turn that Mapquest said is there? Probably something a 21-year-old programmer in Thailand missed while reviewing millions of lines of code.
Knowing the difference between GPS (a system) and a nav system (software) is critical.
