Easily check distance using GPS.
Just click Start, and measure goes.
You can stop the measure and start again any time!
Imagine that you are riding on a bike and want to measure the track you made only in forest. Then you start the measure when you are on the forest, and when you are out - you just stop the measurement. And so on - during the whole bike trip. At the end of the trip you see the global distance which was measured only when you Activated the Distance Meter, so in that case - when you were in forest!