Its all relative. In some countries you can't cut a (normal, everyday) tree down on your own property without asking the government for permission.

Land ownership is indeed an illusion. Your "ownership" of real estate is contingent on the existence of a suite of government apparatus that can verify the authenticity of that piece of paper you call your land title. It's contingent on the existence of a military force that holds the border of your country, such that a foreign entity does not just come in and install a different land office that doesn't recognize that piece of paper you call your land title.

This is one of the core principle of Georgism, that the value and usefulness of a piece of land is tied to the infrastructure that the government has built around it. Therefore the titleholder should pay for the upkeep of that government and infrastructure, hence the idea of the land tax as a single tax.