In spite of its huge scope, rural-to-urban migration is not the main cause of urban growth. For each 60 million new city dwellers in the developing world, 36 million are born to established city dwellers. Only 24 million come from villages, and only half of these have actually migrated – the rest become urbanites because the city has expanded to incorporate their village.
In fact, arrival cities are putting an end to population growth. Some time around 2050, according to the most recent United Nations projections, the population of the world will plateau at nine billion. After that, for the first time in history, humans will stop being more numerous each year.
We have already seen this in quickly urbanizing countries such as Iran, where both rural and urban birth rates have shot down into negative territory.
Average family sizes around the world will fall below 2.1 children, and the problems of crowding and competition for resources will be replaced with the much more sustainable (though still challenging) problems of non-growing population.
Arrival cities accomplish the things that bring fertility rates down – educating girls and women, improving health and creating physical and financial security.
The arrival city is a machine that transforms humans. If allowed to flourish, it will be the instrument to create a permanently sustainable world.
CAUTION: IF NEGLECTED, MAY EXPLODE
When an arrival city's natural functions are blocked or interrupted, however – when its existence is challenged, threatened or ignored – it becomes a place of pent-up frustration. The inevitable conservatism of its transitional culture turns into the furious politics of lost opportunity or the religious extremism of the perpetually excluded.
We have seen terrible explosions out of arrival cities, from the French Revolution to the present: the 1979 Iranian revolution, a pure product of arrival-city neglect; the Hindu-nationalist extremism of Mumbai, born of a political vacuum in migrant slums; the menacing violence of Rio de Janeiro's rural-migrant favelas, where drug gangs took the place of an absent and hostile government.
In Europe, the arrival city has been the centre of conflict – in the flaming outskirts of Paris, the extremist fringes of Amsterdam and the impoverished, backward Turkish enclaves of Berlin.
In France and the Netherlands, these explosions were the results of physical and economic disconnections between the arrival city and the core economy; in Germany and elsewhere, they were caused by a lack of pathways to full citizenship. In both cases, new arrivals were driven into isolation.
By contrast, Canada's arrival cities have been great successes historically, as millions of rural migrants from the Mediterranean, Eastern Europe, the Caribbean and Asia bought up unwanted row-housing stock in Vancouver, Montreal and Toronto and set up classic networks of small business and property speculation.
But Canada got lucky: We had the right housing and the right economy at the right time, and we made citizenship easy, so our governments didn't really need to try.
Today, luck alone will not be enough: Our arrival cities have moved to the far outskirts of cities, where buildings weren't constructed with incoming villagers in mind and links to the core city, both physical and cultural, are scarce.
These high-rise nests of villagers could erupt into trouble if we allow ourselves to repeat Europe's mistakes – or to believe that arrival cities aren't necessary.
IT TAKES A VILLAGER (TO DO OUR DIRTY WORK)
In this age of border controls, high-technology information economies and selective immigration policies, it is too easy for citizens and governments to believe that there should be no reason to have large masses of the developing world's rural poor camped on our urban fringes. This is a dangerous mistake.
It may be politically desirable to slow the influx of arrivals for brief periods, but in the longer term, the arrival city will be a major phenomenon in the West, and its citizens will be the same people who occupy the arrival cities of the developing world. We ought to be planning for and investing in this reality.
The first reason is economic: Countries such as Canada will experience severe labour shortages in the coming decades, especially in unskilled work.