The airport system is divided into two parts, namely the empty side and the land side: the land side includes the terminal, the ground transportation system in and out of the airport, etc., while the empty side includes the runway, taxiway, apron and airport airspace, etc. Taxiway, runway, apron and so on are also called aircraft activity area. Taxiway is the aircraft passage connecting the apron and the runway. It is also the holding buffer area for aircraft on busy runways and tarmac. A runway is a facility for taking off and landing aircraft. The apron is composed of the stand and the apron taxiway, which belongs to the aircraft activity area