What defines the airspace above a nation's land areas and territorial waters?

Territorial airspace is defined as the airspace above a nation's land areas and territorial waters. This concept is important in international law, as it establishes the sovereignty of a nation over the airspace associated with its territory, much like the control a nation has over its land and waters.

Territorial airspace extends typically up to an altitude of 12 nautical miles from the low-water mark along the coast, although nations may have their own regulations that can extend their interest in airspace above this altitude. The concept implies that any aircraft operating within this space must adhere to the regulations and laws of the nation governing that airspace, which can include requirements for flight plans, communications, and permissions to enter.

In contrast, international airspace refers to areas that are not owned or controlled by any single nation, mainly found outside the territorial limits, while controlled airspace pertains to specific areas where the air traffic control is actively managed and is not synonymous with territorial bounds. Free airspace is not a defined term in this context and does not reflect the legal limitations imposed by sovereign nations over their airspace.