WE are just months away from a landmark in the history of humankind.Apparently, 2007 will be the year when for the first time more than half the world's population are city-dwellers.

WE are just months away from a landmark in the history of humankind.

Apparently, 2007 will be the year when for the first time more than half the world's population are city-dwellers.

For a species that has spent most of its existence as hunter-gatherers, and most of the rest as farmers, that's a pretty remarkable statistic.

Of course, as with all statistics, the headline “fact” begs a few questions. The primary one here is how you define a city.

One recent official report in America treated any place of more than 8,000 inhabitants as a city. By that arbitrary measure, Stowmarket counts as a city, but Woodbridge doesn't - unless you include Melton.

A more useful definition would be based on population density - but then too you'd need to decide where to draw the line.

Then there are definitions by land-use and occupation. And that, really, is where it gets interesting.

Until recently, a majority of the world's people were farmers. Now most of us aren't.

When it comes to the really big cities, there isn't much to debate - except where the boundaries are, which makes a huge difference when you try to assess the size of an urban sprawl.

The figures, in any case, can be pretty staggering, and hard to keep up with.

Within my lifetime, London was officially the world's largest city, with a population of about eight million.

Today, London's listed population is actually slightly less than that, but the whole “metropolitan area” comes in somewhere between 12m and 13m - and that barely puts it in the world's top 20.

So what's the biggest city now? Most lists say Tokyo, whose total sprawl is home to nearly 37m people.

But even that may have been overtaken by the Chinese boom city of Chongqing. There are wide discrepancies in the figures for Chongqing's population, largely I think because so many of its people are newcomers and possibly transient, but also because most of it spills outside the official city boundary. The best official figures I can find put it at 30.9m in March 2001 but it is clearly growing fast and nobody knows exactly how big it is now. A recent national newspaper said: "It has grown and grown, becoming what is now the world's biggest municipality with 31 million residents (more people than Iraq, Peru or Malaysia)."

The most up-to-date figures from World Gazetteer give the Top 20 as on this map and say Chongqing is listed at 4,133,663 or 7,572,98 or 31,823,239 depending on where you draw the boundary. I think the middle figure of 7.5m is probably the closest to accurate for the central built-up area, hence its absence from the top 20.

Again, it rather depends where you draw the boundary. By any measure, though, the urbanisation of the world's population is remarkable - and its growth alarming.

The present total of around 6.5 billion human beings is roughly 1bn more than it was only ten years ago.

And even if the growth rate is slowing, there are no serious estimates of a time when the population will actually fall. It will take war, famine or ecological disaster on a cataclysmic scale to bring that about.

It's more than 200 years since the great economist Thomas Malthus made just such a prediction.

He may not have foreseen just how much impact the industrial and agrarian revolutions would have on humans' ability to feed themselves.

His mathematical assumptions may have been faulty, and his idea of how many people the world could hold was undoubtedly much lower than the subsequent reality.

To Malthus's talk of “the perpetual struggle for room and food” we might now add oil, water and designer sportswear.

But he wasn't fundamentally wrong.

Most of humanity's greatest problems come back to one inescapable fact. There is a limit to how many of us the earth can sustain.

Sooner or later we will pass that limit. If we haven't done so already.

REGULAR followers of this column will know that one of my hobbies is photographing birdlife.

I can't claim the credit for this extraordinary photo, though. I've never seen a spoonbill outside a zoo - and I've never seen anything quite like this from any bird.

The picture was taken in South Africa by my friend Dion van Huyssteen.

Dion said: “I was lucky enough to spot this bad boy strutting around the edge of the lake the other day. He was attacking pretty much any other bird that came near him, so I sat down to try to get a shot.

“For about ten minutes I had no success, with most of the fights taking place in the reeds. Then down flew the victim of this photo into the clear water...”

The victim, apparently, got away without much obvious ill-effect. As Dion says, it must be quite hard to do serious damage with a bill that shape.

All the same, it seems startling to see a spoonbill behaving like a human thug. Interesting, that, isn't it?

You can check out Dion's website at www.darkervision.com

Read past columns by Aidan at www.eveningstar.com/columns

Did you know?

Source: wikipedia>

The City of London is a small financial area in Greater London . It is often referred to as just the City or as City or as the Square Mile, as it is approximately one square mile (2.6 square kilometres) in area. Under 9,000 people live there but it has a daily working population of around 300,000.