Google has just announced the addition of a valuable new feature for the Google Maps API (the most popular API in our API directory): reverse geocoding. If you are not familiar with geocoding, it is the process of converting an address into a latitude/longitude pair. Likewise, reverse geocoding is the process of converting a latitude/longitude pair into an address. Developers using the Google Maps API have had access to geocoding since its release in June 2006, and geocoding has been integrated with many of the map mashups developed with this API.

Many mapping APIs offer geocoding, but access to reverse geocoding has been quite limited, especially with the Google Maps API. Prior to the addition of this feature to the API, developers had to rely on third party reverse geocoding APIs and services as well as a JavaScript hack to the Google Maps API.

Pamela Fox over at the Google Geo Developers Blog gives a great summary of this new feature:

A much smaller (but important) percentage of developers will want to use a reverse geocoder to let their map users know the address for a particular point on the map, perhaps to help them fill in a form faster (why type when you can click?!). For those developers, we're now pleased to offer address-level reverse geocoding support to both our HTTP service and the GClientGeocoder class. To make it super easy to use, the interface for reverse geocoding is nearly the same as forward geocoding - the only difference is sending in a lat/lng instead of an address.

Reverse geocoding is available for all 70 countries for which the Google Maps API provides standard geocoding. MeetWays, a site that calculates the halfway between two locations, uses the API to determine the nearest address for the halfway point (and is our Mashup of the Day today):

The API documentation has been updated to include this new feature and there is some sample code available as well. Our Google Maps API Profile includes additional information, including links to over 1,500 map mashups developed with the API.