'''Taiwan''', officially the '''Republic of China''' ('''ROC'''), is a country in East Asia. It shares maritime borders with 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, formerly known as ''Formosa'', has an area of , with mountain ranges dominating the eastern two-thirds and plains in the western third, where its highly urbanised population is concentrated. The capital is Taipei, which, along with New Taipei and Keelung, forms the largest metropolitan area of Taiwan. Other major cities include Kaohsiung, Taichung, Tainan and Taoyuan. With 23.45 million inhabitants, Taiwan is among the most densely populated countries in the world.