Ansan is a city in Gyeonggi Province, South Korea. It lies southwest of Seoul and is part of the Seoul National Capital Area. It is connected t…Ansan is a city in Gyeonggi Province, South Korea. It lies southwest of Seoul and is part of the Seoul National Capital Area. It is connected to Seoul by rail via Seoul Subway Line 4. It is situated on the Yellow Sea coast and some islands lie within its jurisdiction. The largest and best-known of these is Daebu Island.