I recently went on a hiking trip and this issue caused a bit of grief from my friends. At the end of the first day, a few of us tracking our progress with GPS

I recently went on a hiking trip and this issue caused a bit of grief from my friends. At the end of the first day, a few of us tracking our progress with GPS said we had gone about 18 miles. The mapping software we had used (Gaia) had shown we had only made about 12 miles of progress on our 82 mile track. I'm used to GPS overestimating distances since it tends to jump around on the trail a bit (and it still jumps around when you're paused) but the differences throughout the trip were much larger than I would expect. Our 82 mile trip ended up being 104 miles, which my friends weren't really prepared for. Examining the map closer, some of the trails we were on were pretty roughly approximated on the map (way fewer switchbacks, long straight lines, etc.) I'm not allowed to plan our hiking trips anymore...