From United States v. Causby: We have said that the airspace is a public highway. Yet it is obvious that if the landowner is to have full enjoyment of the land

From United States v. Causby: We have said that the airspace is a public highway. Yet it is obvious that if the landowner is to have full enjoyment of the land, he must have exclusive control of the immediate reaches of the enveloping atmosphere. Otherwise buildings could not be erected, trees could not be planted, and even fences could not be run. The principle is recognized when the law gives a remedy in case overhanging structures are erected on adjoining land. 9 The landowner owns at least as much of the space above the ground as the can occupy or use in connection with the land. See Hinman v. Pacific Air Transport, 9 Cir., 84 F.2d 755. The fact that he does not occupy it in a physical sense-by the erection of buildings and the like-is not material. As we have said, the flight of airplanes, which skim the surface but do not touch it, is as much an appropriation of the use of the land as a more conventional entry upon it. We would not doub that if the United States erected [328 U.S. 256, 265] an elevated railway over respondents' land at the precise altitude where its planes now fly, there would be a partial taking, even though none of the supports of the structure rested on the land. 10 The reason is that there would be an intrusion so immediate and direct as to subtract from the owner's full enjoyment of the property and to limit his exploitation of it. While the owner does not in any physical manner occupy that stratum of airspace or make use of it in the conventional sense, he does use it in somewhat the same sense that space left between buildings for the purpose of light and air is used. The superadjacent airspace at this low altitude is so close to the land that continuous invasions of it affect the use of the surface of the land itself. We think that the landowner, as an incident to his ownership, has a claim to it and that invasions of it are in the same category as invasions of the surface. 11 Obviously, it's a tricky issue. It's hard to see if flying a drone over someone else's property is illegal or not. It seems that it might be contingent on altitude, noise, and other forms of disruption.