I made a trip down to Death Valley at the end of March. Since I flew into Las Vegas late in the evening, I planned to pick up a rental vehicle, and spend the night in Vegas before driving to DV. I don't know Vegas well, so I was relying on my smartphone GPS to get me to my lodging. GPS said to turn on a small side street, go 1/4 mile, then turn onto another larger street. The small side street seemed to just lead into some large parking lots. Ultimately it ended at a barricade, preventing making the turn onto the larger street. Apparently the traffic pattern had been changed since the GPS database was compiled.

People need to remember that what we call a "GPS" is really three components. There is the GPS chip itself, which locates one with generally very good accuracy. There is a database of roads, addresses, etc. And there is mapping software that ties the GPS and database together. I think the vast majority of problems come from the database.

These days virtually every nation, state, province, city, county, etc uses location databases together with GIS software to manage their roads. GPS vendors compile all these various databases to use with their GPS products. The problem is that not all of these databases are complete and accurate. Sometimes streets were planned but never completed, but are still in databases. Or, even if the data was originally correct, traffic patterns are changed but databases are not kept up to date (as in my Vegas experience). Various other errors or inconsistencies can get into databases. Considering all the potential problems, I'm surprised that our GPS navigation devices work as well as they do.

The bottom line is that common sense is required. Having a paper map can help, even though paper maps are not always accurate or up to date. (And in many cases, GPS databases were derived from not so good paper maps and charts.) When in town GPS errors usually are just an annoyance, as in my Las Vegas experience. When navigation is more critical, as when I was actually out in Death Valley, it is always a good idea to get some "local knowledge". Try to talk about your proposed route with people who are familiar with the area. As various nautical navigation texts put it: "The prudent navigator should never rely on a single source of information".

In Death Valley, there was one spot I really wanted to visit but skipped. The map and guidebook I had indicated it might be feasible with my vehicle, but after talking to Park Rangers and others who had done the route, I decided I might be pushing my luck with my rental. I'll go there next trip, when I'm driving a more appropriate rig.