Seosan is a city in South Chungcheong Province, South Korea, with a population of roughly 175,000 according to the 2017 census. Located at the northwestern end of South Chungcheong Province, it is bounded by Dangjin City, Naepo New Town, Yesan-gun and Hongseong-gun on the east and by Taean-gun and the Yellow Sea on the west, and is 125 km south of Seoul, 159 km northwest of Daejeon and 34 km northwest of Naepo New Town. Seosan is the hub of transportation of the west coast where the Seohaean Expressway, Daejeon-Dangjin Expressway, National Highways No. 29, 32, 38 and 45 intersect. This city has great traffic conditions towards the metropolitan area and major cities.