By Claire West

Facebook , one of the most-trafficked sites in the world with over 500 million active users, has today launched Facebook Places in the UK.

Places is a location based application using the mobile network and GPS to allow users to see where their friends are and share their location in the real world.

Facebook Places is now available via the iPhone in most of the UK and Europe following a US launch last month.

When you use Places, you'll be able to see if any of your friends are currently checked in nearby and connect with them.

To check in at a Place:
1. Access the Places application on your supported device.
2. Click "Check In."
3. Select the Place where you are from the Nearby Places list. If you don't see the Place name, type the name of the Place where you are into the "Search Nearby Places" box. Alternatively, you can toggle the left-right arrows on the right of the search box to display lists of other Nearby Places.
4. Write an optional description of what you are doing at the Place where you are checking in. You can also tag your friends at the Place where you are.
5. Click the "Check In" button again to share your visit.

Founded in February 2004, Facebook says that 50% of active users log on to the site in any given day and that the average user has 130 friends.

The Places application will compete with Foursquare which currently has 3 million worldwide users