The following paragraph is from the NPS Death Valley website (http://www.nps.gov/deva/planyourvisit/directions.htm):
"Using GPS Navigation
GPS Navigation to sites to remote locations like Death Valley are notoriously unreliable. Numerous travelers have been directed to the wrong location or even dead-end or closed roads. Travelers should always carry up-to-date road maps to check the accuracy of GPS directions.
DO NOT DEPEND ONLY ON YOUR VEHICLE GPS NAVIGATION SYSTEM."
Added notes:
Practically all maps larger than city-level contain longitude and latitude information along the edges; unfortunately, the NPS park maps seem to be universally devoid of this data. Assuming that the automobile GPS-DFI (Global Positioning System – Directions For Idiots) units actually allow one to view your coordinates, it is trivial to determine your location assuming that you are in possession of any sort of road map.
Even if a map doesn't contain any long./lat. information, one can still easily determine their location if the automobile units allow one to also access the coordinates of any two locations on the map (assuming that reasonably large differential long. & lat. coordinates exist between the two). The NPS map of Death Valley, for example, also extends to Panamint Springs, Lone Pine, Beatty, and Death Valley Junction in addition to showing locations inside the park boundries.
