Korean Transportation System-an easy description of the various transportation available

SUBWAY SYSTEM- There are excellent subway systems in Seoul, Busan, Daegu, and Incheon. The subway is the most efficient and convenient way for foreign travelers to get around Seoul and Busan. Station names, ticket counters, and transfer signs are all clearly marked in English as well as Korean, the different lines are color-coded, and all trains have announcements in English and Korean. The subways themselves are clean and efficient, air-conditioned, and have automatic ticket dispensers and convenient bus connections. Each station has a large waiting area and the walls are decorated with various artistic works. Fares are inexpensive, but do vary with service areas, so check the cost for your destination before purchasing a ticket.
< Seoul Subway >

Nine subway lines serve Seoul and its suburbs. The eight lines are color-coded: dark blue for Line 1, green for Line 2, orange for Line 3, light blue for Line 4, purple for Line 5. Line 1 connects Seoul and Cheongnyangni Stations, the two major train stations in Seoul, passing through City Hall and Jongno in the heart of downtown. This line also merges with the surface electric train line of the state-run Korean National Railroad(K.N.R.), linking Seoul to its major satellite cities of Incheon, Suwon, Uijeongbu, and Ansan. Line 2 is a circular route encompassing both sides of the Han-gang River from City Hall through Euljiro, across the river to Jamsil, Yeongdong, and north again to the Sinchon area. Line 3 runs from Daehwa in the northwest to Ori in the south, linking Seoul with its two new satellite cities of Bundang and Ilsan. Line 4, a mirror-image of line 3, is anchored by Danggogae in the northeast and Sadang in the south and is connected to the railroad line to Ansan. Line 5, which passes through central Seoul and runs to Gimpo Airport. The subway line 6 opened in December 2000. Line 7 starts from Jangam in the north goes to Onsu in the southwest. Line 8 starts from Amsa and goes to Moran. Base fare is 1250won for 10km, the charge is added 100 won for each additional 5km.

We quote this content from Korea national tourism organization.