I agree. But why do jobs constantly "bootstrap" themselves in these two centres in a process that seems to feed on itself?
There is a process whereby if urban centre A is larger than the smaller satellites towns B, C, D ... those growth impetus to those smaller towns is slowly, but surely strangled.
What that process is, I am not certain.
I doubt that in an age of mass communications that anyone moves to Sydney, so avail themselves to the opera house! Most Australian's culturalisation orbits about the likes of MKR, and other TV actuality programs, and not much else. And the traffic congestion in the major centres makes rural living a pleasure.
I suspect the answer lies in jobs, and more specifically, household jobs. So not only the job of the primary income earner, but more importantly, the job of the secondary income earner. For in a decentralised centre, the primary income earner's job may well be well satisfied, but trying to couple two satisfying jobs (or more) in a decentralised environment is the bastard!
But there is, I suspect, a strong driver from not only the householders perspective - but employer's perspective too? Big markets create the money, to create secondary demand, & that demand creates jobs, which perpetuates the marketing wheel in a further iteration.
The natural process is to urbanise. Internationally it is the biggest mover of humanity, and we see cities like Mexico balloning to populations of 30 million people, in a country with diverse resources spread across the entire country. In Africa the process is more extreme, as international borders are irrelevant to thwart the energy to urbanise. Kinshasa, Nairobi, Johannesburg, Adis Ababba, and Lagos will all redouble into Mexico Cities in the following decades. Greater Johannesburg & Lagos already have populations of about the 9 to 10 million peoples,
If the EU did not prevent immigration its major cities would all rocket to populations in the 20 plus millions, through donuts of slums that would encircle themselves quite naturally about there peripheries. This so whether those cities prepared for the influx OR not. In fact the first city that did try prepare, would be dooming itself to even more overpopulation, as it would be a signal to the desperate and the starving.
If only we could understand how to create those sustainable satellites!
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As an aside, when we look back on great civilisations we seem to perceive the cities as these great conic achievements, like a towering social hill that rises to a great sophisticated high.
But in truth great cities are not usually driven by noble desires of masses of menials seeking an esteemed enslavement in the Pharaoh's pyramid building teams & schemes, but more like an evil sump or depression that pulls the weak into the vortex with a power and force that exceeds those poor menials powers to resist.
Civilisation feeds, like a bug trapping pitcher plant, on the bugs that are drawn to the allure & hope, but are then incapable of escaping as the greasy sidewalls of the trap prevent their traction, until finally they fall into the gastric soup that devours them in their inner cities.
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