Airspace means the portion of the atmosphere controlled by a country above its territory, including its 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 (however, Air traffic control does not necessarily control traffic operating under visual flight rules within this airspace).
Uncontrolled airspace is airspace in which air traffic control does not exert any executive authority, although it may act in an advisory manner.
 

Section 1: Class A
Section 2​: Class B
Section 3​: Class C
Section 4​: Class D

Section 5: Class E

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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 international, analogous to the "high seas" in maritime law. However, a country may, by international agreement, assume responsibility for controlling parts of international airspace, such as those over the oceans. For instance, the United States provides air traffic control services over a large part of the Pacific Ocean, even though the airspace is international