Foursquare is a mobile application that makes cities easier to use and more interesting to explore. Foursquare lets users "check in" to a place when they're there, tell friends where they are and track the history of where they've been and who they've been there with.
According to REDMOND, Wash (Microsoft Corp):
Windows Live has teamed up with the popular mobile application foursquare to give shutterbugs in Seattle, San Francisco and New York City tips on the best photo locations in their cities.
The Windows Live Photo Gallery foursquare experience provides tips on where and how to take great pictures to share in the three cities, from top tourist spots to hidden gems. In addition to the location, the new experience provides details on how to set up the perfect shot.
See example: Windows Live Photo Gallery & Foursquare Cityscapes