Originally Posted by
JohnJ80
It's not hard to get caught out in bad weather unexpectedly. Anything that reduces visibility can be an issue - fog, rain, night etc... Usually, it's pretty good practice to keep a dead reckoning plot going as well as an electronic one and continually cross check them. Not doing that is when you get in trouble. And when you get in trouble, you're really in trouble and you often don't know which way to go. Pick the wrong one, and you're up on the rocks.
I've seen GPS systems show me that I'm on land when I'm not, probably because I'm behind a high headland and don't have a good view of the satellite constellation. In that case, the GPS gets me in trouble but the DR plot saves me. I've also sailed in a straight line over a probable magnetic iron deposit at night trying to make the finish line and watched the compass do a 360 in about 50 yards (happens often in some geographies). So if you're not skeptical while navigating, you're going to get in trouble at some point. Then there is the whole subject of equipment failures....
This doesn't seem very relevant to cyclists on roads. The issues with use on water are very different (and much more critical).
I can see people on water having "absolute faith" in a GPS. I doubt that cyclists (especially on roads) ever do (except, maybe, in weird rare cases).
There are stories of drivers driving into "lakes" because their "GPS told them too" but that doesn't seem very common considering the high-level of use. These people might drive into lakes without GPS. I wonder if this rare thing is even less common for cyclists.
Originally Posted by
JohnJ80
I'm sure you already know this, but it's not just slot canyons - serious tree cover, riding on city streets with high buildings on both sides, etc... There are innumerable geographies that have reception issues for GPS. It's not a particularly strong signal and, in point of fact, it's relatively easy to have interference with it both physically and electrically (RF).
Sure, this happens but it doesn't seem that common (I rarely see it) or big enough to "cause problems". Seems the biggest issue is missing a turn (but that isn't generally hard to notice).
When I'm using a Garmin for navigation, I have an eye on the map. I usually know about turns before they are announced and can see that I've missed any turns. Many people just rely on the turn announcements, which has issues (easy to miss, can be confusing. sometimes aren't shown when you expect them). In the rare cases where the GPS shows me off the road, it's easy enough to see the road I'm on (that is, this isn't really ever a problem if you look at the map).
Originally Posted by
JohnJ80
Pays to be skeptical. GPS is better than what we had (LORAN etc...) but it's not infallible and it's even not all that good but it works well with other tech that can cross check it (i.e. cellular triangulation etc..).
Where it's being used matters. LORAN suggests you are talking about boats, which isn't that relevant to cyclists. (One will have to be much more careful/skeptical on water.)
Nothing is "infallible" but, from what I've seen over thousands of miles (
cycling and driving), it works well (much, much better than "not all that good").