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Seoul Subway Lines 1 to 9: A Realistic Guide to What Each One Is For

Open a Seoul subway map for the first time and your eyes will not know where to land. Nine colored lines cross and loop across the city, tangled together at transfer stations where three or four colors meet at once. It looks impossible to memorize.

You do not need to. Most visitors end up using two or three lines for their entire trip, and the rest of the map stays background noise. The trick is knowing which lines matter for what.

Line 2 is the green loop that circles the center of the city, hitting Hongdae, Gangnam, and Jamsil in one continuous ring: the line you will ride the most. Line 1, dark blue, is the oldest and longest, running straight through downtown and stretching far out into the suburbs on both ends. Line 9, gold, is the express option: some trains skip stations entirely and cut travel time across the river by nearly half.

That is what is visible on the map. What the colors and numbers actually encode runs deeper.

The Layer
Historical · Cultural · Social Context

One Fare, Several Operators

Seoul’s subway looks like a single unified system, and for a rider it behaves like one: one tap in, one tap out, one fare no matter how many lines you switch between (see the T-money guide for how tapping works). But the ownership underneath is not unified at all.

Lines 1 through 4 were run by a company called Seoul Metro. Lines 5 through 8 were run by a separate company, Seoul Metropolitan Rapid Transit Corporation. These operated as two distinct organizations for decades until a screen-door death at Guui Station in 2016 exposed how fractured safety oversight had become between them. The public backlash forced what years of cost-cutting proposals could not: on May 31, 2017, the two merged into a single operator, Seoul Transportation Corporation (서울교통공사), which now runs lines 1 through 8.

Line 9 sits outside even that merger. Its first phase opened in 2009 under a private consortium, built and operated for profit under a build-operate arrangement with the city, before later phases were absorbed into public operation. It is why Line 9 still runs its own express-train schedule, a feature none of the other lines have: it was designed by an operator competing for ridership, not a public utility filling in a grid. Numbering here does not follow geography. It follows the order each line opened, which is why Line 1 runs through the historic downtown core and Line 9 cuts underneath the Han River on the newest, straightest route in the system.

End of Layer

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