911 services should use Google Maps! Seriously, this is a non-trivial problem. GPS data alone does not have the precision. However from all the data that Google

911 services should use Google Maps! Seriously, this is a non-trivial problem. GPS data alone does not have the precision. However from all the data that Google has collected from driving those mapping vans around, Google should have accurate topography data (elevation is important for making GPS more precise for non planar geographies) and should have building locations through, say, visual analysis of the street photos. With the additional inputs it can make a better guess of your most likely location. The improvement is probabilistic, not guaranteed. And it is only available if your phone is capable of communicating at the right level with the service (provided by your app in the Google Maps case) that has the enhanced information. But even then, in multi-story buildings GPS may be hard to acquire in the first place. See https://en.wikipedia.org/wiki/Enhanced_9-1-1#Wireless_enhanced_911 https://en.wikipedia.org/wiki/Enhanced_9-1-1#Wireless_enhanc... for general information.