Shanghai Metro - longest in the world?

Currently, Shanghai claims that with the opening of line 10 last month, Shanghai Metro became the longest such system in the world.

Of course, that depends on what counts toward that total.

Not including portions run by Korail and Incheon Subway, Seoul's Metropolitan Subway system runs 314 km. However, that is counting some track that runs outside of the boundaries of the city of Seoul, and does not include some that is actually within the city's boundaries. So 314 km is too short. Counting every line that could possibly be considered part of the system, the subway is 755 km long. Of course, that ends up trips that never even enter the province where Seoul is located and that are between towns of less than 100,000.

So Shanghai runs a lot of trains that I hear are clean and fast, and you can probably go anywhere you might want to on them. But not necessarily any better than in, say, Paris, which strictly defines what is the metro and what are the suburban commuter trains.

(Also, the maglev to the airport is cool, but very few people take it because the maglev is more expensive than some airplane tickets and the ordinary subway is fast and comfortable enough for most people.)