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.

Oido (Korean: 오이도) is an island on the West Coast region of South Korea's Gyeonggi Province. It is an area of Siheung stretching from north to south with low hills under 72.9 m (239 ft). Oido has shell mounds throughout the whole area, with the largest of the mounds located on the West Coast. The Oido shell mounds are the only remains of the exchanges between the North and South Neolithic cultures of the Korean Peninsula. The mounds also provide information on the Neolithic area's changing coastal environment.