Everybody seems to forget that those wonderfully precise GPS coordinates have an underlying error on the order of 20 meters, more or less, kinda sorta.
A friend took a bicycling vacation, riding about 50 miles a day, and camped overnight. Evidently his GPS tracker developed a nasty case of insomnia and wandered all over the campsite: the first two points might be actual motion, but the rest were in the wee hours of the morn when he says he was sound asleep.
It became painfully obvious over the course of his journey that you cannot depend on continuous satellite uplink coverage. Even though he was riding on rail trails and open roads, the every-ten-minute position uplink to low earth orbit would vanish for hours at a time. The GPS tracker has a 911 button, but it might be a long time before they could figure out where he was.
Memo to Self: get those GPS-to-APRS gadgets built for our bike trips…