Busan (부산 or 釜山(Korean pronunciation: [busʰan]), officially Busan Metropolitan City), Latinized Pusan before 2000, is South Korea's second largest metropolis after Seoul, with a population of approximately 3.6 million. The population of the metropolitan area, including the adjacent cities of Gimhae and Yangsan, is approximately 4.6 million. It is the largest port city in South Korea and the world's fifth busiest seaport by cargo tonnage. The city is located on the southeastern-most tip of the Korean peninsula. The most densely built up areas of the city are situated in a number of narrow valleys between the Nakdong River and Suyeong River, with mountains separating some of the districts. Administratively, it is designated as a Metropolitan City.