Microsoft has announced a web service that allows Wi-Fi users to obtain details of their location and access to local information.

The MapPoint system is located on Microsoft's Virtual Earth service, a database that includes details of Wi-Fi locations in the US.

Microsoft claims to have gathered the information using special cars that have trawled the country to map the exact location of Wi-Fi networks.

The software giant has collected the unique identifier, known as the Media Access Control address, which is broadcast by every Wi-Fi network.

By putting these addresses into a database Microsoft believes it has created a system that can act as an alternative to GPS to give positioning information. Users will be able to locate their position to within 30 metres.

The service initially covers the US but is being developed for the UK and other countries.

In a clear shot across Google's bows, Stephen Lawler, general manager for MapPoint, said: "When you're in a unfamiliar city and need to find a Chinese restaurant or ATM within walking distance of your hotel, traditional internet searches will not give you the information you want.

"Virtual Earth lets people see what it's like to be in the location and easily explore what they can do there."

Microsoft has used low-flying aircraft to create a database of aerial photographs, in contrast to Google which is using satellite photography.