Seoul Metropolitan Subway, often called Seoul Subway, is metro network that connects Seoul and suburban areas in its vicinity. It is referred as longest metro system in the world, and second busiest metro system in the world, just after Tokyo Metro.
The system is consisted of 9 numeric-named lines (Line 1 ~ Line 9), Gyeongui Line, Bundang Line, Shinbundang Line, A'REX, Jungang Line, Gyeongchun Line, Suin Line, Incheon Line 1, Everline and U Line.
Since 2010, all stations have smartphone like 46-inch touchscreen kiosk, so that passengers can look at the map, make free phone calls, or get tourist information. All lines use special RFID cards, such as T-money, or NFC technology to impose traveling fee.