According to International Civil Aviation Organization (ICAO), Federal Aviation Administration (FAA) and Civil Aviation Administration of China (CAAC), any structure that exceeds 200feet above ground level or 30m above the ground elevation and 150m above the airport elevation within area that 20km width and 40km length from the center of airport must be marked with aviation obstruction light (aircraft warning lights). The structure could be high rise buildings, towers, chimneys, power lines, wind power plants and bridges ect.