Microsoft has launched a new mapping service, dubbed Virtual Earth 3D, to rival Google Earth.

The online application lets users view a three-dimensional map of, initially, 15 US cities when they use Live Search. Users can also view two-dimensional maps, both aerial and bird’s eye views.

Although Microsoft is said to be investing hundreds of millions of dollars in the project, the company plans to monetise it through virtual billboard advertising.

The software uses both high-res images taken from the air and new images that are being transmitted by vans equipped with cameras driving through cities all over the US, so that users will eventually be able to browse cities at street level in 3D. Although only 15 US cities, including San Francisco, Los Angeles, and Atlanta, are available now to view, Microsoft plans to add 5000 worldwide.

“By helping people visualise information in far more useful and intuitive ways, Virtual Earth 3D takes search to an entirely new level”, Bill Gates commented. “The immersive 3D experience provides a more powerful and engaging interface that delivers better experiences not only for consumers, but also for developers and advertisers.”

Microsoft is offering the Virtual Earth 3D application programming interface to developers to use in their own searches and applications on various websites.