By Jo Twist
BBC News science and technology reporter
Imagining what our cities will look like in the future has long been a favourite pastime of the Hollywood movie industry.
On the whole we are presented with striking images of glass and metallic towering structures, flying cars and technologically smart everything.
Many of world's big cities are surrounded by shanty towns
Dystopic pockets of inequality and dirt inhabit the not so shiny bits.
Ask a gathering of leading thinkers in the worlds of architecture and design, and you get a rather different picture.
Some 70 million people a year migrate from the country to cities. That is about 130 a minute, says Robert Neuwirth, author of Shadow Cities.
Many of these set up home in squats, put together from scarce materials, if put together at all. There are a billion squatters in 2005. By 2050, that figure will reach three billion.
At this rate, our future cities may turn out to be quasi-temporary, low-tech shacks, missing the basics of human life, such as water and electricity, still belching out the waste of fuels that warm the globe.
"The issue is about neighbourhoods," Mr Neuwirth told delegates at TED (Technology, Entertainment and Design) conference in Oxford, UK.
"Cities have to engage these residents because they are building the cities of the future."
View from above
Globalisation has done its best to push constant migration deeper into the urban from the rural with the promise of work.
But cities have failed to cope with it, physically, emotionally or mentally. They cannot sustain the flow and they are not sustainable and fair places to live.
Visualising globalisation which continues to run rampant across parts of the globe has come a step closer with Google Earth.
It brings places far from your desk right onto the computer screen with a couple of clicks.
"What is amazing is that you really can, from your desk, explore the globe," explains Stefano Boeri, lecturer, author, editor of Domus magazine, and architect.
"You can fly around then you can get closer to parts you want to see. This website is a combination of the virtual node of thousands of satellite images."
Satellite images, he says, are one attempt to visualise, represent and decipher globalisation and its marks on cities.
"But what we really understand and see when you use satellite images, first of all, is our ambition."
But it is a view from above that is apparently objective, he says. It is still a view from a certain distance from the physical environment you attempt to decipher.
New city China
Internationally renowned designer, sustainability architect and author of Cradle to Cradle, William McDonough, argues that we can only think of our future cities if we think about what our intention is as a species.
The question for designers of what is dubbed the Next City is how to love all species all the time.
Mr McDonough's ideas for the Next City are about to be played out in China where his company has been charged with building seven entirely new cities.
William McDonough's city hall roof garden in Chicago
His book has been adopted as government policy in China, which needs to house 400 million more people in the next 12 years.
The cities he has planned are a far cry from Milton Keynes.
Everything in his cities is designed from the molecule up. They meet the usual requirements for cost, performance, and function. But they also mean business when it comes to ecological intelligence and social justice.
"The goal is a safe, healthy, just world, clean air, soil and power, that is elegantly enjoyed.
"In the 70s we saw the hegemony of fossil fuels. So what would be the next design philosophy we would want to work with?"
He looks at the Next Cities as objects of human artifice. They can grow, they can breathe, and they can be ecologically sound, just as trees, forests, and gardens are.
They can use energy, expel waste, and reproduce in ways that nature intended without destroying everything else around them.
"In biology, growth is good. If we could do something where growth is good, that would be a way of thinking of a good operating system for design," he says.
Waste as energy
The images he shows of what he plans look like gardens of Eden.
"We lay the city out so everyone can move in parks without crossing traffic, the buildings have daylight lighting, the university is at the centre, and with hi-tech connectivity."
The buildings and all around it work like biological, growing beings, photosynthesising and producing and re-using their own energy.
Waste is energy in Mr McDonough's Next City vision; methane is used to cook food. A quarter of the city's cooking will be done with gas from sewerage.
"The energy systems will be solar energy. China will be largest solar manufacturer in the world," says McDonough.
To top the Next City in McDonough's thinking, the soil will be moved onto the roofs. The city will be inhabited by species and the top of the city will be green.
His approach to city design may be the stuff of some people's eco-science fiction novel. But it shows that cities can change - humans can change the way they do things.
It may not mean the city is transformed magically into a just city that is a cure-all for global warming.
But, he says, the Stone Age did not end because humans ran out of stones. It ended because it was time for a re-think about how we live.