The Google Distance Matrix API is a service that provides travel distance and time for a matrix of origins and destinations. The information returned is based on the recommended route between start and end points, as calculated by the Google Maps API, and consists of rows containing duration and distance values for each pair.
The Distance Matrix API has the following limits in place:
100 elements per query.
100 elements per 10 seconds.
2500 elements per 24 hour period.
The API uses RESTful calls and responses are formatted in XML and JSON.