Attempting to identify the world's largest subway system
can prove difficult, given that there are many ways of measuring it such as length of track or number of daily passengers. One comprehensive way of figuring it out is by looking at the sheer number of stations across different networks worldwide. The folks over at CityMetric
carried out an analysis in 2015, finding that New York's subway comes first by number of stations with 468 in total.
Interestingly, it would only actually have 421 "by international standards" as the network has several "station complexes" consisting of two or more stations together. The next three entries on the list are all Asian with Shanghai and Beijing coming second and third respectively. Seoul comes fourth with 311 stations while Paris rounds off the top-5 with 303.