Busan (Officially Busan Metropolitan City), formerly spelled Pusan (Korean pronunciation: [pusan]) is South Korea's second largest metropolis after Seoul, with a population of around 3.6 million. The Metropolitan area (includes adjacent cities of Gimhae and Yangsan) population is 4,399,515 as of 2010. It is the largest port city in South Korea and the world's fifth busiest seaports by cargo tonnage. The city is located on the southeasternmost 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. The Busan metropolitan area is divided into 15 major administrative districts and a single county.