South Korea, officially the Republic of Korea (Hangul: 대한민국; hanja: 大韓民國; RR: Daehan Minguk, lit. The Republic of Great Han; ROK), and commonly referred to as Korea, is a sovereign state in East Asia, constituting the southern part of the Korean Peninsula. The name Korea is derived from the ancient Kingdom of Goguryeo, also known as Koryŏ. It shares land borders with North Korea to the north, and oversea borders with Japan to the east and China to the west. Roughly half of the country's 51 million people reside in the Seoul Capital Area, the second largest in the world with over 25 million residents.