The result is expected to be an online map that allows web surfers to land in a city from the sky, walk its streets and navigate its hotels, shops and attractions without ever having to visit in person.
The rival schemes, costing hundreds of millions of pounds, are based on Google Earth, the search engine’s existing 2-D photographic map of the world, and Microsoft’s Virtual Earth, a similar system.
Last month, Microsoft launched Virtual Earth 3D, which has detailed three-dimensional replicas of the centres of 15 American cities, including New York and Los Angeles. There are plans to add more than a dozen in Britain over the next few years.
Both services currently rely on detailed satellite images from Nasa and other space agencies and governments, which enable users to zoom in from 200 miles in space to pictures of the roof of their own home or of elephants roaming the African plains.
Microsoft is now commissioning photographers to take millions of pictures of urban landscapes from planes, vans and motorbikes. The images are patched together using digital imaging software to create 3-D buildings users can enter, walk past or fly by.
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Google is taking the cheaper option of inviting users to create its virtual cities. In March, the company bought SketchUp, an internet tool that lets people create their own 3-D images of buildings. It plans to add the best of these, which include British landmarks, to Google Earth later this year.
As the rival schemes develop, buildings will become interactive, enabling users to “enter” them, obtain information, buy goods inside and talk to other “visitors”.
Eventually, landscapes such as forests and mountains could also be included.
The move may bring about a transformation in how people use the internet. Instead of relying on traditional search engines, in which they enter words into boxes on screen, users would be able to navigate the world using a virtual replica of how it appears in real life.
They could, for example, “walk” the streets of Manchester online or choose items from a supermarket aisle from their living room while gossiping with fellow shoppers about the prices. Greg Sterling, an internet analyst, said: “A seed is being planted that could grow into a range of things that will be very interesting.”
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Microsoft and Google launched their online photographic mapping services at the end of 2005, since when it is estimated they have each been downloaded more than 100m times.
Microsoft’s early 3-D service has few extras beyond traffic information and adverts.
In Britain, the company is showing 3-D models only of the outsides of landmarks such as the Tower of London and the London Eye. In future features may include a route planner, which gives a virtual run-through of a journey.
The company plans to develop the package quickly.
David Graham, Microsoft’s UK search business manager, said: “We are committed to creating a technology which allows you to find anything through a 3-D interface. You will be able to zoom in on a hotel, find out what the prices are, see what the foyer looks like.”
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Google Earth’s approach is based on how it has already developed. Users contribute their own content to appear alongside photographs of their local areas. This can include pictures, weather or traffic information, often updated on a daily basis, creating a “community” feel.
Chikai Ohazama, joint founder of Google Earth, said: “It could offer people a much greater understanding of the world around them. Being able to fly to New York using the program and look at the buildings will give people an insight into the place they couldn’t get otherwise.”
To view sample 3-D pictures of buildings, go to:
Google 3D
Microsoft Virtual Earth 3D