Seoul is the capital of South Korea. With a municipal population of over 10.5 million, and a metropolitan population totaling over 20.5 million, Seoul is by far South Korea's largest city and one of East Asia's financial and cultural epicenters.
China, officially known as the People's Republic of China, is a vast country in Eastern Asia about the same size as the United States of America with the world's largest population, 1.355 billion according to the 2013 census.
South Korea, officially the Republic of Korea is a country in East Asia. South Korea occupies the southern half of the Korean Peninsula, with North Korea to the north, China across the sea to the west and Japan a short ferry ride to the southeast.