In Kyoto half the population of the entire metro area lives within city limits. In a comparably sized American city like Philadelphia it might be a quarter. Or you might have something like Atlanta, with a city that has 1/3 as many people as Kyoto in a metro area that has twice as many.

The net result is that a good subway system in Kyoto can serve a majority of the metro population, while that is not true for Philadelphia or Atlanta. (That is true even though Kyoto is not particularly dense--closer in Atlanta to density than to Philadelphia.)

Perl4Ever was expressing doubt that an area of a million or two people could support rail. I think Kyoto is an excellent counterexample to this claim, and the rail lines are what propel the density as people want to buy homes that are walking distance from a train station.

But let's look at Boston instead. Population 700,000 in the city limits; 4.8 million in the metro area, so about one seventh lives in the city proper.

http://www.rochestersubway.com/images/photos/boston_subway_m...

While perhaps not as developed as Kyoto, that's still a very healthy rail system. And its first subway was built in 1897 when it had a population of just about half a million.

"an area of a million or two people could support rail. I think Kyoto is an excellent counterexample to this claim"

The metro area in which Kyoto is located is around 20 million people. The metro area of Boston is almost 5 million people, you say. These are not counterexamples to what I was trying to communicate. I don't really think my comment was as hard to understand as you make it seem.

The bus system is also excellent.