Outdoor positioning is what we consider GPS (Global Positioning System) and A-GPS (Assisted GPS). Using satellites, cell towers, and Wi-Fi databases, outdoor positioning does a reliable job of pinpointing you within approximately 20 meters . Standard GPS is a great solution for outdoor positioning products, such as road navigation, photo tagging, and location based searches.
While it is a great solution for many products, GPS suffers from one fundamental problem. The signals sent by GPS satellites are relatively weak. So weak in fact, that these signals cannot penetrate the structure of most buildings. This makes positioning within a building very difficult, if not impossible. With the help of AGPS, you can usually estimate a position within general proximity of the building you are in, but you would never be able to take the next step to achieve accurate indoor positioning using these methods.