Chongqing is a dense and smoky inland city, the heavy-industry, high-rise home to over 30 million people. It is to China what Chicago was to 20th-century America, or Manchester to 19th-century England, and it’s growing at an extraordinary rate. Every day a tide of 1,500 new people washes in to Chongqing. Every day an extra 1.5 million square feet of floor space is constructed for new residents. It’s a vast megalopolis, a megacity of the sort that will soon take over the world.

I met Mr and Mrs Zhang on the day they first arrived in Chongqing from their rural village. It had taken them almost 10 years to raise enough money to move and required outrageous sacrifice: They pooled together their accumulated cash from years of sweated labour in motorcycle-parts factories, and had paid the full purchase price of 150,000 yuan (£14,000) for a clean and elegant three-bedroom apartment, turning them, legally, into city-dwellers. In the next few months they will bring their parents over from the village, shutting the farm down and ending their family’s millennia-long connection to the fields.

The Zhangs are the archetypal people of the 21st century, and we ignore their story at our peril. For the defining force of this century, almost certainly more significant than war, recession and perhaps even climate change, will be the huge and final shift of human populations from rural areas to cities. It’s a crucial issue — one that every politician, every economist and sociologist should be considering. Because the mind-boggling fact is that we will end this century as a fully urban species.

It sounds frightening, especially to the lucky, affluent, Western middle classes who dream of nothing so much and so often as moving to the country. But our urban future shouldn’t be an alarming prospect. The migration to cities will create enormous tensions, conflicts and cultural clashes, but it also means a vast reduction in poverty and suffering, and an end to the major ongoing concern of human history: continuous, unrestrained population growth.

In Europe, North America, Australasia and Japan, the move to the largest cities is now fully complete. The rural areas represent between five and 25 per cent of the population, and those numbers have generally been stable for decades. For the most part these people live in villages by choice and not by force of necessity. But what about the countryside? What about farming? Well, fewer than five per cent of Western populations are now employed in agriculture — sometimes as little as two per cent — and this is enough to produce more food, at low cost, than their urban populations can consume. Now that the poor half of the world is once again experiencing food shortages, it is desperately important that this high-yield agriculture develop in the poor half of the world.

And, indeed, this is the transformation that is now taking place in South America, in Asia, and gradually but inexorably in Africa. At the moment, only 41 per cent of Asians and 38 per cent of Africans live in cities; the rest are largely subsistence farmers, people whose entire livelihoods depend on the vicissitudes of weather, fertilisation and crude credit relations. They are on the land not because it is a better life, but because they are trapped.

This is changing fast. Between now and 2050, the world’s cities will absorb an additional 3.1 billion people.

The population of the world’s countryside will stop growing around 2019, according to the UN Population Division’s more conservative estimates, and by 2050 will have fallen by 600 million because of migration to the city. India’s rural population, one of the last to stop growing, is set to peak in 2025 at 909 million, and shrink to 743 million by 2050. Each month, there are five million new city-dwellers created through migration or birth in Africa, Asia and West Asia.

By the end of 2025, 60 per cent of the world will live in cities; by 2050, more than 70 per cent; and by century’s end the entire world, even the poor nations of sub-Saharan Africa, will be at least three quarters urban. And this point, when the entire world is as urban as the West is today, will mark an end point. Once humans urbanise, or migrate to more urban countries, they almost never return.

Why is it so important to think about this now? Well, rural living is the largest single killer of humans today, the greatest source of malnutrition, infant mortality and early death.

Urban poverty may force a mother to send her child into the street to sell goods; rural poverty will cause that child to die of starvation. People do not, as an almost universal rule, die of hunger in cities. Urban incomes everywhere are higher; access to education, health, water and sanitation as well as communications and culture are always better in the city.

Urbanisation doesn’t just improve the lives of those who move to the city; it improves conditions in the countryside, too, by giving villages the finance they need to turn agriculture into a business with salaried jobs and stable incomes. These remittances are very much responsible for the decline of poverty and the rise of commercial agriculture in these countries.

The dramatic declines in the number of very poor people in the world around the turn of this century (world poverty rate fell from 34 per cent in 1999 to 25 per cent in 2009) were caused entirely by urbanisation: people made better livings when they moved to the city, and sent funds back to the village.

One last, crucial, calming fact for the anxious. It can feel to a native city-dweller as if the floods of newcomers to a city mean that the population as a whole is expanding wildly, beyond our ability to control it. But when villagers migrate to the city, their family size drops, on average, by at least one child per family. So, the urbanisation of the species will, in the end, be our salvation.

The endless search for a parking spot in the city may be a thing of the past—in San Francisco, at least. After years of preparation, the city is now rolling out SFpark, a high-tech new system that will set the price of parking spots according to supply and demand.

To reduce congestion, San Francisco is aiming to have one spot open at all times on every block. Here’s how the plan works: A network of wireless sensors let the city keep track of which parking spots are empty. If a particular block never has available spots, the city raises the meter rates until it does. In places where parking is plentiful, rates fall. As an added bonus, this information-age system lets residents check the rates and availability of parking online before deciding to drive.

In the first phase of the rollout, now underway, the city is installing 190 new meters in the Hayes Valley neighborhood. That will be followed by 5,100 more new meters in seven other areas.

The system is expected to increase revenue from parking meters, but decrease revenue from traffic tickets. How this will balance out for the city budget is unclear. Also unclear: Just how high the prices will go. Will there be $10 per hour parking?

What it should do, however, is keep the streets from being so crowded with cars and help people avoid needless driving. Average motorist, meet Adam Smith.

The lights are going out all over America — literally. Colorado Springs has made headlines with its desperate attempt to save money by turning off a third of its streetlights, but similar things are either happening or being contemplated across the nation, from Philadelphia to Fresno.

Meanwhile, a country that once amazed the world with its visionary investments in transportation, from the Erie Canal to the Interstate Highway System, is now in the process of unpaving itself: in a number of states, local governments are breaking up roads they can no longer afford to maintain, and returning them to gravel.

And a nation that once prized education — that was among the first to provide basic schooling to all its children — is now cutting back. Teachers are being laid off; programs are being canceled; in Hawaii, the school year itself is being drastically shortened. And all signs point to even more cuts ahead.

We’re told that we have no choice, that basic government functions — essential services that have been provided for generations — are no longer affordable. And it’s true that state and local governments, hit hard by the recession, are cash-strapped. But they wouldn’t be quite as cash-strapped if their politicians were willing to consider at least some tax increases.

And the federal government, which can sell inflation-protected long-term bonds at an interest rate of only 1.04 percent, isn’t cash-strapped at all. It could and should be offering aid to local governments, to protect the future of our infrastructure and our children.

But Washington is providing only a trickle of help, and even that grudgingly. We must place priority on reducing the deficit, say Republicans and “centrist” Democrats. And then, virtually in the next breath, they declare that we must preserve tax cuts for the very affluent, at a budget cost of $700 billion over the next decade.

In effect, a large part of our political class is showing its priorities: given the choice between asking the richest 2 percent or so of Americans to go back to paying the tax rates they paid during the Clinton-era boom, or allowing the nation’s foundations to crumble — literally in the case of roads, figuratively in the case of education — they’re choosing the latter.

It’s a disastrous choice in both the short run and the long run.

In the short run, those state and local cutbacks are a major drag on the economy, perpetuating devastatingly high unemployment.

It’s crucial to keep state and local government in mind when you hear people ranting about runaway government spending under President Obama. Yes, the federal government is spending more, although not as much as you might think. But state and local governments are cutting back. And if you add them together, it turns out that the only big spending increases have been in safety-net programs like unemployment insurance, which have soared in cost thanks to the severity of the slump.

That is, for all the talk of a failed stimulus, if you look at government spending as a whole you see hardly any stimulus at all. And with federal spending now trailing off, while big state and local cutbacks continue, we’re going into reverse.

But isn’t keeping taxes for the affluent low also a form of stimulus? Not so you’d notice. When we save a schoolteacher’s job, that unambiguously aids employment; when we give millionaires more money instead, there’s a good chance that most of that money will just sit idle.

And what about the economy’s future? Everything we know about economic growth says that a well-educated population and high-quality infrastructure are crucial. Emerging nations are making huge efforts to upgrade their roads, their ports and their schools. Yet in America we’re going backward.

How did we get to this point? It’s the logical consequence of three decades of antigovernment rhetoric, rhetoric that has convinced many voters that a dollar collected in taxes is always a dollar wasted, that the public sector can’t do anything right.

The antigovernment campaign has always been phrased in terms of opposition to waste and fraud — to checks sent to welfare queens driving Cadillacs, to vast armies of bureaucrats uselessly pushing paper around. But those were myths, of course; there was never remotely as much waste and fraud as the right claimed. And now that the campaign has reached fruition, we’re seeing what was actually in the firing line: services that everyone except the very rich need, services that government must provide or nobody will, like lighted streets, drivable roads and decent schooling for the public as a whole.

So the end result of the long campaign against government is that we’ve taken a disastrously wrong turn. America is now on the unlit, unpaved road to nowhere.