Methodology — The Subway Index

Source: Seoul subway ridership by line and station (서울시 지하철호선별 역별 승하차 인원 정보) — card-gate ridership records published on the Seoul Open Data Plaza by Seoul Metro (서울열린데이터광장. Data month: 2026-07. Retrieved 2026-08-29.
How the ranking works: For each station we sum boardings and alightings across the month and divide by 31 days. Stations served by several lines are merged into one entry (Seoul Station’s five lines count as one station), with the lines listed alongside.
Update cadence: The source publishes daily records, archived monthly in the first days of the following month. We refresh with each complete month.

Limits worth knowing before you cite this

Gate taps are not people in the station. Transfers between lines inside the paid area never touch a gate, so a huge transfer hub can rank lower than its actual crowds suggest.
One month is one season. This snapshot is 2026-07; a university station looks different in exam season, and a beach-line station in summer.
Coverage is the Seoul card system. Lines outside it (some suburban extensions and other operators’ segments) are not in this dataset, so “busiest in Seoul” means busiest among its 529 covered stations.