The world's cities are growing all the time, and in France some are being modelled by computer for the purposes of urban redevelopment.

Fifty years ago only a third of us lived in urban areas. Now half of us, that is three billion people, are born and brought up, live and die, amid the concrete and glass.

Cities look after our every need: we live, work and holiday in them.

They have truly become machines for living in.

But what if we want to tinker with the machine and develop a sensitive area like, say, the sea-front at Cannes?

If I was a planner then I might want to know what effect that development is going to have on the traffic, the noise level and the pollution.

Now planners can turn to technology, which enables them to test drive an entire city.

Future renovations

Cannes - the place where Hollywood goes on holiday - has itself become a special effect.

A 3D mock-up was commissioned by the city so planners could peer into the future and see how developments will affect the chic resort's delicate balance.

It is just the sort of tool that administrators, like those meeting at the recent Global Cities conference in France, could all be making good use of in a few years' time.

Take a project like lighting.

The traditional approach to showing conference delegates how lighting can transform a city is to construct a film-set. That's the approach taken by electronic giant Philips.

"Lighting plays a very important role. You can take very old buildings which are not so nicely finished and with a bit of lighting you can make them look very good," says Jaap Schlejen of Philips Lighting.

"People feel safer, people feel better, more at home and of course, they would also like to visit that city a bit more."

But if you really want to see how the light is going to play on a specific place then you need a 3D mock-up.

Model for comparison

France's Centre for Building Technology (CSTB) has made light work of Place du Bouffay in Nantes.

This is no craggy old corner in need of a facelift, but a historic tourist spot that demands delicate handling.

They have done a similar job for Paris's famous bridges.

Each place has had detailed studies of the materials from which they are made and the computer-generated model reveals how various surfaces react to different light.

CSTB's Jacques Martin says: "It's important to emphasise that this is a physical simulation. That means we put real light sources into it and we take account of the real materials.

"For example, if there is a wall in stone, we take account of how much exactly that material reflects the light. The other thing we do is take account of the shape of each lamp and how it emits light, and we put that in the model."

CSTB has also carried out a detailed analysis of noise levels around Place du Bouffay.

Pull up the 3D surround sound-armchair in their lab and you can take an audio tour of the town.

That, and the ability to demonstrate the passage of pollution around a city, makes this a useful potential tool for showing those dubious about a development project exactly what the end result will be.

Jacques Martin adds: "We are supplying tools so everyone can understand what's going to happen and discuss the project.

"What's more, we can show everything at the same time. We can listen to how the project will affect the ambient sound: the noise from the cafe, music from shops, the bird-song, people talking.

So we can compare the acoustics, show how the light will change and even look at how the project will affect pollution."

Complementary methods

It is a far cry from the architect's drawing board, and while the aim is to put the individual in the picture of planned projects, there is still no substitute for getting out of the office, taking in the air and seeing and hearing it for yourself.

Architect Jan Gehl says: "You can never animate in a machine how people would like to sit on a bench or not like to sit on a bench.

"It will always be a balance between using really genius technological tools to short-cut the working processes, to be able to assess quicker what you've thought up, and studying the real-life situation and using your own senses directly with the environment."

It has always been people who have had to adapt to the constraints of where we live and where we work.

Now, perhaps, we can tailor our surroundings to take more account of what we want.