If my GPS experiences are anything to go by, big stuff (buildings and mountains) and cold (possibly heat too?) make GPS inaccurate enough that it would be pretty much useless. Up high in subzero temperatures on a mountain we would get strange coordinates back due to (I assume) the mountain blocking or reflecting signal somehow. And that was when it worked - sub zero with a big wind chill and the batteries would last about 10 seconds, then back under the jacket it had to go to warm up. This has been on multiple brands of hardware. Things may have improved since this experience as it was 5 years ago.