This is a remarkable feat. Amazing.

I’d like to add an interesting metric: density of subway/metro stations as measured by number of stations per square kilometer.

In European cities,

City, Metro System, Stations, City Area (km²), Density (stations/km²):

1. Paris, Metro de Paris, 244, 105, 2.32

2. Berlin, U‑Bahn only, 173, 892, ~0.19

3. London Underground (London Tube), ~270, 1,572, ~0.17

4. Madrid, Metro de Madrid, ~300, 605, ~0.50

Paris takes the lead, not just in Europe but globally, with ≈2.32 stations/km². Madrid has a dense network too (≈0.50), though well behind Paris. Berlin (U‑Bahn only) and London have much lower densities (~0.17–0.19). Rome’s iconic metro is relatively sparse in terms of station density compared to other major European and Asian cities.

Here’s how European and Asian cities stack: 1. Paris (~2.32 stations/km²) 2. Seoul (~1.27) 3. Madrid (~0.50) 4. Tokyo (~0.46) 5. London (~0.17) 6. Berlin (~0.19) 7. Hong Kong (~0.09) 8. Shanghai (~0.06) 9. Rome (~0.057)

Seoul is highest among major Asian metro systems in terms of station concentration, making it the city in Asia with the densest metro network per square kilometer. Seoul has 768 stations in its metropolitan subway system spread across the city proper area of 605 km². By comparison, Tokyo’s combined metro (Tokyo Metro + Toei) has around 286 stations over ~621 km, giving a density of about 0.46 stations/km². Beijing has 523 stations but the city covers about 16,411 km²—yielding a much lower density (~0.03 stations/km²). Shanghai’s figure fluctuates due to rapid expansions: 409 unique stations from early 2025 data.

In addition to density, another interesting metric is the number of street-level entrances (exit/entry points). Counting just stations ignores how many access points are available to the public. More entrances = better coverage, shorter walking distances, improved accessibility, especially in dense urban zones. Examples from Paris are: Saint‑Lazare station (Lines 3, 12, 13, 14) has 11 entrances. Hotel de Ville (Lines 1 & 11) has 7 entrances. Madeleine station (Lines 8, 12, 14) has 5 accesses with 7 separate entrances. Alesia station (Line 4) has 6 entrances. Opera station (Lines 3,7,8) has 3 main entrances.

On average, Paris Metro stations have approximately 3–6 street-level entrances, with major hubs having 7–11. Paris doesn’t just have many stations, it maximizes them with multiple entry points, making its system exceptionally accessible over its territory. Seoul also scores similar in accessibility due to its exit-rich stations, especially in dense areas. Other major metros (Tokyo, Madrid, London) lag when entry points are factored in.

I did not include US cities but I believe New York City might be notable.

> 4. Madrid, Metro de Madrid, ~300, 605, ~0.50

> [...] Madrid has a dense network too (≈0.50), though well behind Paris.

As a native of Madrid, I must point out that using the nominal surface area of the municipality of Madrid (~605 km²) is misleading for these purposes due to the Monte del Pardo [0] and Soto de Viñuelas [1], two fenced off forest areas covering around 180 km² between them. The impact of these areas on the nominal surface area of the city is visually obvious when you compare the outlines of Madrid and Paris administrative areas:

+ Madrid: https://www.openstreetmap.org/relation/5326784

+ Paris: https://www.openstreetmap.org/relation/7444

As a result, the relevant surface for estimating the density of Metro stations in Madrid should be at most ~425 km². While one may arguably also want to exclude the Bois de Boulogne and the Bois de Vincennes from the surface area of Paris, even the "de-Pardo'd" surface area of Madrid still contains significant non-urban areas such as the Casa de Campo forest, large non-built-up areas, and even most of its airport.

(In any case though, after this pedantic "well ackshually", I must also point out that a few Madrid Metro stations actually fall outside of its municipal limits. I would get out more, but I live in a town without a Metro)

[0] https://en.wikipedia.org/wiki/Monte_de_El_Pardo

[1] https://en.wikipedia.org/wiki/Soto_de_Viñuelas

Is Paris 6 times smaller than Madrid and 15 times smaller than London? Seems suspicious to me. What exactly is the boundary of this "area" and how does it relate to the subway network?