title: How does iPhone do geo locating?
body: <p>Since there are 3 generations of iPhone, what's the mechanism of their geo locating(WiFi, GPS, any other ways?)? I am doing iPhone development recently so I want to make a deep understanding of this.</p>
  
  <p>(I want a list of all methods of locating and a specific introduction)</p>
  
  <p>Thank you</p>