Your cell phone knows where you are.

Armed with a smartphone full of location-based applications, you can cue up Yelp reviews and Groupon offers for the nearest restaurants, get turn-by-turn directions there from Google Maps, and then use Foursquare to share your location with followers on Facebook or Twitter. Whether through GPS capability or cell-tower triangulation, today’s mobile devices gather and put geolocational information to use in a multitude of ways.