how smartphone obtains its geographical postiion = GPS + WPS (wifi positioning system)
buildings blocking gps signal → wifi positioning sysystems → use databases of wifi APs (independently maintained by various internate companies liek google, apple, microsoft) → each db contains info abt milliosn of wifi APs including each AP’s SSID + estimation of its geo location
tri-laterization
indoor localization → determine a device’s location with a building relative to known locations
using cell tower triangulation (3 towers) → determine a phone location to within an area of about 3/4 square mile