BuddyPress.org

Location data from the Foursquare API isn’t very useful unless you’re only dealing with Foursquare users. The data is way too centric.

Google Places API is easy to pull in.
Their documentation is very comprehensive.
Hook into wp_enqueue_scripts and use wp_register_script and wp_print_script to pull it in.
Then call it in a template.
How to get, store and use the Location data is up to you.