Taiwan, officially the Republic of China (ROC), is a country in East Asia. Neighbouring countries include the People's Republic of China (PRC) to the northwest, Japan to the northeast, and the Philippines to the south. The main island of Taiwan has an area of 35,808 square kilometres (13,826 sq mi), with mountain ranges dominating the eastern two-thirds and plains in the western third, where its highly urbanised population is concentrated. Taipei is the capital as well as the largest metropolitan area of Taiwan. Other major cities include New Taipei, Kaohsiung, Taichung, Tainan and Taoyuan. With 23.7 million inhabitants, Taiwan is among the most densely populated countries, and is the most populous country and largest economy that is not a member of the United Nations (UN).