It's generally regarded that Hong Kong has the best subway in the world. There are many reasons for this, but one cannot be overstated: Hong Kong's geography. A huge portion of the city consists of long thin urban corridors sandwiched between mountains and the sea. As a result, Hong Kong need concentrate its funding on only a few subway lines to support a huge portion of the population.

This good article aside, I wonder if the same thing is true about Japan when we're talking about long-distance trains. Compared to France or Germany, Japan is basically a stick. A very large chunk of the populace lies on a single train line running from Kagoshima up to Hakodate, running through Fukuoka, Hiroshima, Osaka, Kyoto, Yokohama, Tokyo, Sendai, etc. So you can slap a single bullet train line there and service all of them.

I think you're broadly correct and that's definitely a reason, and I have another example to support it.

Mumbai too has a very similar structure (the core city is basically a peninsula that goes north-south). Our railway lines run N-S as well, with (till the recent Metros) feeder roads connecting them.

Mumbai is also one of the most densely populated cities in the world (#2 by some metrics).

Our local railways have an annual ridership of 2.26 billion [1]. Pretty much everyone agrees they're vital to the city.

1 - https://en.wikipedia.org/wiki/Mumbai_Suburban_Railway

The Hong Kong Metro is also very well planned, architected, and generally well run operationally. So much that the MTR corporation actually offers international consulting services. And for two decades, they have consulted with many mainland Chinese metro systems, hence it's no coincidence that the Shanghai and Shenzhen metros both look and feel very similar to HK's.

Even if the geography isn't thin it seems like there are major US cities you could draw a route through that would have similar population distributions. Or at least good enough for the economics to work.

That is a good point but I think it doesn't apply everywhere.that has a similar shape. New Zealand has a similar shape but without railways interconnecting cities. You cannot cross the country, the islands, or even regions by train.

I think this could be a variable to contribute to a good coverage and infrastructure... but there are probably more factors involved.

Yes. You get a lot of bang for your buck as far as the number of people served. Hong Kong is less than half the area of Rhode Island, but the populations are 7.5 million for Hong Kong and 1.1 million for Rhode Island. Small area plus high population density is the situation where trains are most valuable.

Geography like that does help a lot, it’s part of the reason it’s so easy to do really good high-speed rail in Italy over somewhere like Germany that is way more spread out. But it’s only half the picture, you also need the political will to get it built!

I'm sure geography helps, but it's certainly not the driver for good train service design. Cities in Japan are definitely not laid out in thin lines, and there's not just a few routes in any given city. I was living in Nagoya back in high school, and its train lines are sprawling.

Side note, there actually isn't one shinkansen from Kagoshima to Hakodate, that route would take you on 5 different shinkansen lines: Kyushu, Sanyo, Tokaido, Tohoku, and Hokkaido. But I get your point.

That’s arguably irrelevant to anything except the Shinkansen.

Switzerland has 8m people. Bay Area has 8m people. Switzerland is 1/4th as densely populated as the Bay Area (4x the size) yet they have 10x better transportation

California is also like this for the most part. Bay Area has 8 m, Los Angeles area has 17 m, and San Diego area has 3 m. 28 out of 39 live in those three. Straight line.