The FAA thinks that if it is designed for flight and not touching or connected to the ground it is in federal airspace and they have say as to what you can and cannot do there. A "drone" that is hovering one inch off the ground is in the national airspace system, not your backyard. The only case, so far, where this was challenged (many, many years ago), the court recognized that a property owner's rights only went up to 83' AGL.
The 500' thing comes from the regulation that requires a pilot to keep his aircraft 500' away from things like people, vehicles, and buildings (except when landing or taking off). This can be vertically or laterally. It is legal to operate your aircraft at less than 500' AGL in "non-built up areas". You can often see planes at less than 500' over water.
Of course, what the law says and what actually happens in real life aren't always the same.
I'm reading this differently, but I'm also not an attorney. The FAA regulates your behavior in the air, including 0-500'. And Congress has established airspace above 500' as public right of way. But teh space below 500' is the exclusive domain of the land owner. From the Wiki article "...but the Supreme Court rulings and space treaties are clear. A landowner's domain extends up to at least 365 feet above the ground. see
Causby v US (1946)" That Supreme Court decision established that flight operation in that lower window is considered a "taking", just like seizing your property for a new highway.
And it doesn't matter how old the decision is. It still stands.
Now there is a clear distinction between operating over private land vs over land where you already have a right of access. For example, the ocean and most inland water bodies are public access, so that extends to the low flight zone over it. The same would be true for other public lands, or lands with public right of way. So you could fly over public roads, but not over the adjacent property that its private.
It really distills down pretty simply. If you have right of access to the land, you have similar right of access to the low flight space over that land. If you do not have right of access to land, then you also don't have right of access to the low air space over it. To fly over private land, you need to go over 500' (365' in rural areas).
Also, don't confuse lands that are open to you, with lands where you have a right of access. The two things are very different. Lands open to you are still full controlled by the landowner, and they can revoke permission at any time, and can similarly decide if they want to extend access to the airspace that they control. So don't assume that if you have access to the land, you also have access to the airspace. A right of access means that you have a right to access or cross the land, and nobody can deny you access. That's very different from being voluntarily invited to use land.
Using the example of a drone circling your boat in an anchorage, that's no different than someone circling your boat in a kayak. The waters are public and anyone can go anywhere they want, within limits of regulations. But someone circling your house is another thing all together, assuming you own the surrounding land where the drone is operating.
