The OP may be as smart as he thinks he is, but he appears to not know GPS too well
"High-end users boost GPS accuracy with dual-frequency receivers and/or augmentation systems. These can enable real-time positioning within a few centimeters, and long-term measurements at the millimeter level."
GPS.gov: GPS Accuracy
There are many sources of GPS information but this one summarizes pretty well. With good ground mapping of altitude and a GPS received that is multi-frequency and fast enough quite reliable location accuracy within <10cm is quite common today. People in this thread, including the OP seem to be equating typical smartphone GPS with current state of the art. I will not suggest that use of GPS can eliminate need for sign-reading and other local data, nor that GPS will function perfectly without very clear reception of satellite signals.
When combined with receptors for GLONASS, the Russian GPS equivalent, more dependable high accuracy measurements are possible because of adding more satellite positions to the geometric calculations. That sometimes helps also because the US maintains the right to intentionally degrade the GPS signals, although they've not done that very much. The biggest weakness of these systems is not accuracy. It is that they are military systems used civilly by the generosity of the military masters.
In practice today GPS can and does quite dramatically reduce the requirement for other data in open areas, and even in areas that have intermittent obstructions such as mountains, forests and cities. Even in those areas combining GPS with inertial navigation can maintain those levels of precision and accuracy. BTW, deductive ( often incorrectly called 'dead' reckoning cannot substitute because it assumes maintaining an established course, almost never a good assumption on a road.
Because of the complexity of these issues multiple techniques can be effectively employed. IMHO most people who says they know the exact answer to a given question usually don't actually understand the question very well. People who do understand the question usually are a bit modest because they usually understand that new information can change established assumptions.
In short, video clips probably help but they certainly are not anything like a complete answer. They obviously contribute information, but are transitory in their value because of the dynamic nature of surface navigation.
As usual I point out I am not an expert. I have used GPS since 1987, and kept studying the advances since then. So I do think I'm pretty knowledagble, for a layman.
