Capital-Centric Countries and Regions
Here is a table of various developed countries, as well as some regions of the US, based on how dominated they are by their largest respective cities. The table includes the percentage of the population in the top metro area, and the ratio of the top metro area’s population to that of metro areas 2-4. Different countries have data from different years, but within each row, the data is from the same year. Of course the definitions of metro areas are not consistent from country to country, but I’ve tried to use the more expansive definitions where they are available.
| Area | Pop’n | 1st % | 1st/2nd | 1st/3rd | 1st/4th |
| South Korea | 48.8m | 48% | 6.45 | 9.34 | 16.26 |
| California | 37.7m | 48% | 2.36 | 5.76 | 7.46* |
| US Northeast** | 65.8m | 34% | 2.55 | 2.92 | 3.39 |
| Japan | 127.8m | 28% | 1.9 | 4 | 6.38 |
| Texas | 25.7m | 27% | 1.11 | 3.14 | 3.77 |
| UK | 59m | 23% | 3.72 | 5.36 | 5.96 |
| France | 61.4m | 20% | 5.71 | 6.79 | 9.56 |
| Germany | 82.3m | 14% | 1.93 | 2.08 | 2.17 |
| Spain | 45.6m | 13.5% | 1.35 | 2.67 | 4.51 |
* Sacramento excludes the one county it has in Nevada.
** The Northeast includes Washington, the states to its north and east, and its suburbs in Virginia and West Virginia.
I could not find data for Switzerland, but the Canton of Zurich is 17% of national population; including the neighboring cantons of Schaffhausen, Zug, and Schwyz (all with Zurich S-Bahn service) raises this to 22%; including also Aargau, also with Zurich S-Bahn service, raises this to 29%.
The takeaway from this table is that our usual notions of which regions are more capital-centric (France, UK, Japan, South Korea) and which are less (Germany, most regions of the US) are more than just about the capital’s share of the population. Germany’s difference with France is not just the largest metro area’s share of the population; it’s also the difference between political centralization around Paris and the polycentric economy of Germany, and this is seen in the second-city shares. (And on top of this, the Rhine-Ruhr region is itself highly polycentric, and the stricter definitions of metro area break it into three.)
In the Northeastern US and California, we see huge largest-cities, but also strong second cities. This is true both demographically and politically, and this is why we can expect travel between Los Angeles and San Francisco or between New York and Washington to be much more symmetric than in France or the UK.
Pedestrian Observations 
Australia belongs in that list, but state by state rather than countrywide.
State by state, Australia is incredibly capital-centric. The same is true of Canada province by province, except for Alberta and Saskatchewan.
New Brunswick?
Forgot about it, sorry.
Which is why a national ranking would be deceptive ~ such as comparing Sydney to Melbourne, Brisbane and Perth, when each are the center of a large hinterland with the majority of the population of each region located in the state capital city.
The only thing that works or matters in Australia is Sydney-Melbourne, with Canberra tossed in because it’s sort of for free.
I could see an extension to Newcastle. Is Brisbane worth it?
Intercity? Melbourne to Adelaide is a much more popular connection than Richard might expect; the economic ties are suprisingly large. Probably doesn’t really justify “true high-speed”, but does justify reliable “faster than American speed” rail.
I disagree with this idea of breaking large (land area) countries into smaller jurisdictions and comparing them to entire countries when it comes to transportation, considering that even fully “border-less” international travel within Schengen Area in Europe, for instance are still subject to many factors that influence their demand despite geographical proximity.
It’s less a matter of breaking areas for transportation, and more a matter of figuring out perceptions of centralism. California is not perceived as very LA-centered, even though LA is close to half the state’s population; the Bay Area manages to exercise a fair amount of political counterweight, despite its much smaller population.
The comparison I wanted to make was with the Midwest, which is less Chicago-centric if you measure either first-city population share or first-to-lower-city population ratios, but is perceived as a hub-and-spoke region. You could realistically refer to Detroit and Minneapolis as provincial cities around Chicago; you could not do the same for San Francisco around LA. And the Midwest is politically and culturally a fairly coherent region – it’s not monolithic, far from it, but it views itself as a single region, with ill-defined borders with the Plains, the Northeast, and the South (Pittsburgh, Kansas City, and Louisville are all border cities). I just didn’t have easy fully comparable data – but the metro area ratios are 1.87, 2.66, and 3.37.
There is some transportation implication, regarding travel symmetry. A perfectly balanced corridor, like Dallas-Houston, can expect symmetric peak travel. So the interesting thing is why, based on any normal understanding of the economic geography of various countries and regions, Japan has asymmetric travel between Tokyo and Osaka at least as far as local trains are concerned, while California most likely has symmetric travel between LA and the Bay Area. (Likewise, most people’s bias, including mine, is to assume Northeastern and Californian travel is more symmetric than Midwestern travel.)
Alon, could you explain a bit more about the pattern of asymmetric travel between Tokyo and Osaka? I may be able to find an answer if you can tell me where you saw the data.
To be honest, I just looked at Tokaido Shinkansen schedules. There are a lot of peak-hour Kodama runs to Tokyo – 5 tph sustained over 2 hours, from arrival at Tokyo just after 7 to just after 9. The base is just 2 tph. With Osaka, counting trains that stop at Gifu-Hashima and Maibara regardless of how they’re called, the base is 2 tph, one Kodama and one Hikari, and the peak is 3 tph sustained over 1.5-2 hours. So it just looks like Osaka is not a big high-speed commute destination. Could be that longer-distance travel is perfectly symmetric, of course.
Thanks for the clarification. I think your statement that Osaka is not a big high speed commute destination is the main answer. Tokyo dominates its surrounding region much more than Osaka, which otoh has more major subcenters (Kobe, Kyoto), as well as the Tokai(Nagoya) region being relatively nearby. Also, on the stretch of Tokaido shinkansen between Maibara and Shin-Osaka, the parallel 1067mm gauge Tokaido Line offers a good, frequent commute service (the “new rapid service”) with 120km/h top speeds.