It is actually the newly released Yahoo! Internet Location Platform, which allows applications to share predefined location identifiers, known as WOEIDs.

You can use the platform to match a WOEID to a place on earth, find parent and child relationships to that location and neighboring areas.

The Yahoo! Internet Location Platform provides a resource for managing all geo-permanent named places on Earth. Our purpose in creating the Internet Location Platform is to provide the Yahoo! Geographic Developer Community with the vocabulary and grammar to describe the world’s geography in an unequivocal, permanent, and language-neutral manner.

The Internet Location Platform is designed to facilitate spatial interoperability and geographic discovery; users can traverse the spatial hierarchy, identify the geography relevant to their users and their business, and in turn, unambiguously geotag, geotarget, and geolocate data across the Web.