Geo AR apps are easy to write because all you need to provide is a collection of objects that have Latitudes and Longitudes. These can come from anywhere, for example a Bing restaurant search, a Flickr photo search or a Wikipedia article search. The framework then takes care of managing sensors and tracking where the user is in relation to the reference points. It can show where the points are in relation to user from a top-down perspective (on a map) or it can show where the points are as a virtual lens into the real world.