What exactly does it mean by the "lateral boundaries of the surface area"? It almost seems to me that the floor of the Class E airspace is irrelevant, based on my interpretation, and that you need ATC authorization to fly underneath Class E airspace (as designated for an airport)... Anyone care to clarify this for me? I'm studying for the aeronautical knowledge test, plus I got a warning on DJI Go a few weeks ago that I was approaching Class E airspace even though I was flying at 100ft. It got me curious.