linguistic:voice_change, information:extraction
Geography

Seoul is in the northwest of South Korea. Seoul proper comprises 605.25 km (233.69 sq mi), with a radius of approximately 15 km (9 mi), roughly bisected into northern and southern halves by the Han River. The river is no longer actively used for navigation, because its estuary is located at the borders of the two Koreas, with civilian entry barred. There are four main mountains in central Seoul: Bugaksan, Inwangsan, Naksan and Namsan. The Seoul Fortress Wall, which historically bounded the city, goes over these mountains. The city is bordered by eight mountains, as well as the more level lands of the Han River plain and western areas.