Antisocial Network

You've been tasked with building an application that helps users avoid people they'd rather not see. After much thought you realize that the best approach is to compare your current location to that of your "friends." You don't want to rely on proprietary data because that means user growth and that takes a long time.

You've assessed the main social networks and you've decided that Foursquare, Instagram, and Twitter will provide you with the most up-to-date location data.

Which API endpoints from Foursquare, Instagram, and Twitter could you use to build your application?