I'm REALLY not qualified to answer, but apparently a GID is about 1/12th of a kilowatt-hour. It's shown on several screens in LeafSpy as the unit of energy currently in the battery. The long answer is this thread:
When I charge to 100%, the Guess-O-Meter (the dashboard display) says about 90 miles. If I leave home by the route that is gently uphill, it drops to 84 miles in a couple of miles. Even if I didn't drive carefully, I think I could get that far driving around the city on my usual routes, so let's say 84 miles is the worry-free range of my car at 35 MPH and no big net uphills. Edit: note that "big" is not that big a hill. Consider how much harder it is to ride a bike up a moderate grade to appreciate that idea. But if you turn around and come back down that hill, you can recover at least some of that energy, so closed-loop routes with some hills are OK.