Seoul is the capital and largest city of South Korea. With over twenty million people, Seoul is one of the world's largest cities. It is also the world's second largest metropolitan area, the Seoul National Capital Area - which includes the major port city of Incheon and satellite towns in Gyeonggi-do, having almost 23 million inhabitants. Almost half of South Korea's population lives in the Seoul National Capital Area, and nearly one quarter in Seoul itself, making it the country's political, cultural, and economic centre. As a Special City, it is administered directly by the national government. The city is located on the basin of the Han River in the country's northwest. The North Korean border lies about 50 km to the north. Seoul first appears in history in 18 BC, when the Baekje kingdom established its capital Wiryeseong in what is now around Songpa-gu, southeastern Seoul. Modern Seoul descends from the Goryeo-era city called Namgyeong, which then became the capital of Korea during the Joseon dynasty. As a major financial and cultural center, Seoul is considered a global city. The city has hosted the 1988 Summer Olympics and the 2002 FIFA World Cup. In 2007, it was listed as the fifth most expensive city in the world and the second most expensive in Asia. In recent years, the Seoul Metropolitan Government has undertaken major environmental projects, including the nearly $1 billion restoration of Cheonggyecheon. At the same time, the city has promoted the Seoul Digital Media City, the world's first complex for high-tech digital technologies in multi-media, IT, and entertainment, and the proposed future site of the world's second tallest building.
There are two international airports that serve Seoul. Gimpo International Airport, formerly in Gimpo but annexed to Seoul in 1963, was the only international airport for Seoul since its original construction during the Korean War. Other domestic airports were built around the time of the war, including at Yeouido. Upon opening in March 2001, Incheon International Airport on Yeongjong island in Incheon changed the role of Gimpo Airport significantly. Incheon is now responsible for almost all international flights and some domestic flights, while Gimpo serves only domestic flights with the exception of flights to Tokyo International Airport (Haneda) in Tokyo and Hongqiao Airport in Shanghai. This has led to a significant drop in flights from Gimpo Airport. Meanwhile, Incheon International Airport has become, along with Hong Kong and Singapore, a major transportation centre for East Asia. The 2005 AETRA passenger survey, jointly administered by the IATA and Airports Council International, voted it the best airport in the world. It was named by Skytrax as the world's 5th best airport for 2006. Incheon and Gimpo are linked to Seoul by highways, and Gimpo is also linked by subway (line #5). The Incheon International Airport Railroad, a rail line connecting Incheon Airport to Gimpo Airport opened in March 2007, but the line to Seoul Station in central Seoul will take at least a year more to open. Shuttle buses transfer passengers between Incheon and Gimpo airports.
Seoul's bus system is operated by the Seoul Metropolitan Government, with four primary bus configurations available servicing most of the city. Seoul has many big intercity/express bus terminals. These buses are connecting Seoul and cities all around Korea. Major bus terminals are Seoul Express Bus Terminal in Seocho-gu Central City in Seocho-gu Seoul Nambu Terminal, also in Seocho-gu Dongseoul Bus Terminal in Gwangjin-gu Sangbong Terminal in Jungnang-gu To reduce air pollution in the city, the government is planning to change over seven thousand of Seoul's diesel engine buses with natural gas by 2010.
Seoul has eight subway lines that interlink every district of the city with one another and with the surrounding area. The majority of the population now uses the public transportation system due to its convenience and low cost. With more than 8 million passengers a day, Seoul has one of the busiest subway systems in the world. In addition, in order to cope with all of these transportation modes, Seoul's metropolitan government employs several mathematicians to coordinate the subway, bus, and traffic schedules into one timetable. The 10 lines are run by Korail, Seoul Metro and SMRT.
Seoul is connected to every major city in Korea by railroad. Seoul is also linked to most major Korean cities by the KTX bullet train which features a normal operation speed of more than 300 km/h, making commuting between cities extremely convenient for commuters and tourists. Major railroad stations include: Seoul Station, Jung-gu - Gyeongbu line (KTX/Saemaul/Mugunghwa-ho), Gyeongui line (Saemaul/Commuter) Yongsan Station, Yongsan-gu - Honam line (KTX/Saemaul/Mugunghwa), Jeolla/Janghang lines (Saemaul/Mugunghwa) Yeongdeungpo Station, Yeongdeungpo-gu - Gyeongbu/Honam/Janghang lines (Saemaul/Mugunghwa) Cheongnyangni Station, Dongdaemun-gu - Gyeongchun/Jungang/Yeongdong/Taebaek lines (Mugunghwa)