Which line is used to identify suitable building area locations on airports?

The building restriction line is the correct choice because it is specifically designed to demarcate areas where construction is either limited or prohibited to ensure safety and operational efficiency at the airport. This line helps prevent the placement of structures that could interfere with aircraft operations, particularly near runways and taxiways, where they might pose safety hazards.

The primary purpose of the building restriction line is to create a buffer zone around critical areas of the airport, thereby allowing for the safe operation of aircraft and minimizing the risk of accidents. By adhering to the guidelines set by this line, airports can manage development in a way that maintains safe distances from flight paths and infrastructure.

Other options, while related to airport layout and safety, do not serve the same function as the building restriction line. For instance, the safety zone pertains to areas around specific facilities, the runway threshold line marks the beginning of the runway for aircraft takeoff or landing, and the clear zone line defines areas around runways that should be kept free from obstacles but does not specifically control building locations.