Airspace means the portion of the atmosphere controlled by a particular country on top of its territory and territorial waters or, more generally, any specific three-dimensional portion of the atmosphere.
* Controlled airspace exists where it is deemed necessary that air traffic control has some form of positive executive control over aircraft flying in that airspace.
* Uncontrolled airspace is airspace in which air traffic control does not exert any executive authority, although it may act in an advisory manner.
Airspace may be further subdivided into a variety of areas and zones, including zones where there are either restrictions on flying activities or complete prohibition of flying activities.
By international law, the notion of a country\'s sovereign airspace corresponds with the maritime definition of territorial waters as being 12 nautical miles (22.2 km) out from a nation\'s coastline. Airspace not within any country\'s territorial limit is considered