They tell you to park in an open area, without tall buildings or mountain ranges, so that you have the best chance of having 3 satellites in position just for those satellites & your vehicle to triangulate
.............................................
When i still worked for the State of California
We were sent out in several teams to record every single Highway Storm Drain in our area.
We had a GPS locator mounted on the pickup truck that i was driving
Another person on the team had a GPS locator that he wore on his back
The 3rd Team member was an engineer, he marked everything down in Notes & on 2 laptops.
There was usually 3 & sometimes 4 satellites above us in San Diego
At other times there were only 2 satellites, we could still receive a signal, but it was not a verified signal, we needed 3 satellites to be verified.
When there was only a single satellite, we just located a tree or other place to stretch our legs, because that data feedback was worthless.
After a day or 2 of recording drains, we noticed that the satellites & the time of day corresponded, with a 4 or 5 minute time difference each day.
Like one day we would only have a single satellite at Noon to 12: 25
The next day we would only have the single satellite at 12:04 to 12:29