a map based dead reckoning protocol for updating location information
According to the Google Maps website, the Web mapping service uses map and location data that is available online as well as information businesses and other locations provide Google directly.
Since Google depends on the accuracy of its information sources, the accuracy of mileage between locations varies.
The method described here uses Google Maps’ Geocoding API.
The free version of this only allows 2500 lookups per day, I easily ran into this limit during development.