Spatial entities provided by Yahoo! GeoPlanet are referenced by a 32-bit identifier: the Where On Earth ID (WOEID). WOEIDs are unique and non-repetitive, and are assigned to all entities within the system.
An integral part of GeoPlanet is the WOEID (Where On Earth IDentifier), a unique 32-bit reference identifier, now assigned by Yahoo!, that identifies any feature on Earth. WOEID is used by a number of web applications, such as zWeather.GeoPlanet has a java library that provides access to the GeoPlanet API, including WOEIDs.