- I used Wikipedia. It has its limitations, but I wanted something I could put together fast.
- Specifically, I started from Wikipedia's List of metro systems, because it has an easily sortable list.
- I chose number of stations, not system length, or ridership, or even opening date, because the particular item of interest in this map is the station names.
- To get city founding dates, I looked at the Wikipedia page "History of (city)" where there is one, the city page if not. Again, limitations. But again, fast.
New York City: 456 (including the New York City Subway, Staten Island Railway, and PATH)
Seoul: 377 (all operators, but not including Incheon)
London: 315 (including DLR, which the preceding map does not include)
Tokyo: 293 (including Tokyo Metro, Toei Subway, and Rinkai Line, but not Yokohama)
Mexico City: 195
Of these, only eleven were in existence as a city in 1014, although not necessarily under their current names: Seoul, London, Paris, Madrid, Beijing, Barcelona, Delhi, Guangzhou, Osaka, Vienna, and Milan.
A number of fairly old cities just fail to make the cut: Oslo, founded around 1000 CE, has 97 stations. Nanjing, founded in 495 BCE, has 92 stations. It'll likely have eight more built within a couple of years. Chongqing is also eight stations shy of a hundred, and is also likely to break a hundred soon. Hamburg has 91. It was repeatedly destroyed between 810 and 993 CE (and later, for that matter), but evidence exists to support it having been around before 1014.
Founding dates for many cities are just estimates, so the cutoff is quite arbitrary. So is the cutoff of a hundred stations. Finally, just what constitutes a metro system is something endlessly debated on the list's talk page. (Seriously. The list has eighteen pages of talk archives.)
(Edited for slightly more clarity, I hope.)