What is a vertical boundary?

Vertical boundary simply refers to height limit in airspace. However, there is no international agreement or law that states the vertical boundaries of a sovereign state. Borders between FL600 and above are undefined and unregulated.

Most countries set their airspace as high as 100,000 feet (30,000 meters) and many others set theirs as high as 525,000 feet (160,000 meters). The outer space is set to begin at 100 km above the earth’s surface but the US considers anyone who has flown above 80 km to be an astronaut.

In most cases, satellites can operate at an altitude of over 100 km without triggering frontier violation.