[franciscop]

The geography of the "cities" is very different though (look at the density of population maps provided), where "Tokyo Metropolitan" is one third pure mountains, then one third low-density living (think L.A.) and then one third what people normally thinks of the city of Tokyo, all of these in a sausage-like shape, while "Greater London" grows in a circle and so it's a circle-ish area.

See this image with the labels, we should compare the green one instead of the 3 of them. Ideally "Tokyo" would be something more like the purple one, but the purple one is nothing. So we have "23 wards" (green), or Tokyo Metropolitan (the 3 together), neither of which is the best comparison, but def the green one vs London is much better than all of them (the purple dashes are how I think London would look like approx):

https://imgur.com/a/nCmkE80

[throwaway2037]

To complement your post: To be clear, no one with a deep understanding of Tokyo area considers anything outside the "23 ku's" as Tokyo. Really, Okutama, Tokyo (two hours west of world's busiest train station: Shinjuku) is comically rural -- literally, there are big mountains and small family farms that grow wasabi (delicious!). Yes, the province of Tokyo is enormous and includes lots of protected nature (and lovely hiking trails!), but when most people say "Tokyo" they mean the central 23 cities ("ku's"). If you want to get more specific, Tokyoites sometimes discriminiate between inside and outside the loop train line called Yamanote line. It is definitely the sense of urban and ex-urban in Tokyo.

[bombcar]

Yeah, every "city" has a point at which you're clearly "outside the city" but what you count changes depending on who you talk to.

https://www.google.com/maps/place/Okutama,+Nishitama+Distric...

The "gray areas" on a map like this might be a decent "rule of thumb" but even those can be misleading. The best way to determine it is talk to a local.

The other amusing thing is that if some city is famous tons of areas around it will often claim it in name if not address; you'll find "New York Shop" in New Jersey from time to time, especially if doing mail-order business.

[GuB-42]

And even for the "green" area, a good part of it is not that dense. I mean, it is still packed, but most of it is made of small 2 story houses rather than large apartment complexes and high rise buildings.

The real dense part that looks like the pictures of Tokyo you have most likely seen is around the Yamanote line, a train line that circles an area that is about 1/10 of the green area.

[franciscop]

I see it everyday since I live here, no need for pics :)

But yeah I agree, one of the first things that surprised me is that you can walk for 20 mins (in the right direction) from any major train station and find yourself in a tiny 1-2 stories houses area.

[ouid]

If you want to take a more principled approach to size here, you should use a metric that corresponds to how humans interact with the region. Pick a point to call the center and find all the points with a round trip time less than some number.