One more thing to consider is most of these "bigger" drones will be loitering at fairly high altitude, so the only problem with these UAV's is climb and descent. Just like tethered balloons their base of operations will be marked on the sectional chart. The local departments such as fire and rescue would probably use the much smaller drones and these will be flying within the cities at low altitude. If a pilot follows altitude requirements he must fly 1000 feet above and 2000 horizontal of the highest object in a congested area.