Q. How do “indoor” maps work? I thought GPS had a hard time getting signals if your phone wasn’t outdoors in a clear area.
A. The United States Global Positioning System (GPS) currently uses a system of 31 operational satellites transmitting radio signals to receivers on the ground. Once the GPS device on the ground receives signals from four or more satellites, it can use geometry to calculate its three-dimensional position on the earth’s surface.
According to the federal GPS.gov website, GPS-enabled smartphones are typically accurate within a 16-foot radius under open skies — but that precision falls off if the phone is near bridges, tall structures and trees. Signal blockage from being inside a building or underground (in a subterranean parking garage, for instance) can also prevent a map app from pinpointing your location.
Some indoor maps are simply static floor plans of the building for easy reference, much like a directory map at a shopping mall; flight tracker apps, for example, often include airport guides for travelers. For maps that do provide fairly accurate positioning indoors, information from your phone’s Wi-Fi network data, special Bluetooth beacons and radio-frequency identification systems — or even dedicated hardware installed by the place you are visiting — can help mark your spot.
Apple Maps, Google Maps and Microsoft’s Bing Maps all have some indoor maps available, typically for large public places (like airports, museums and shopping centers), that you can use for directions and navigation. To see an indoor location that has been mapped, zoom in; Apple Maps uses a blue Look Inside button.
A Microsoft Research blog post, “Path Guide: A New Approach to Indoor Navigation,” describes some of the current approaches to interior mapping and how its own Path Guide app for Android works for creating user-recorded indoor maps. Some venues also map their own interiors for customer service, and often for tracking user movement around the space — especially in a store.
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