Yahoo! Placemaker is not a geocoder, so addresses in requests are resolved to the smallest bounding Place, usually a town or a postal code. Also, WOEIDs are not assigned to individual house numbers or street names.
Yahoo! Placemaker delivers bounding boxes and centroids of named places. This information is not definitive, and we make no claims to be the authority on the center of a place, its best routing point, nor the approximation of its extents. We provide coordinates only to assist users in finding the place on a map, and zooming to the correct extents.
Postal codes, such as US zip codes or UK postcodes, are assigned by postal authorities within a country for the purpose of expediting mail delivery, and do not necessarily align with administrative areas or cities in that country. For example, in the US, a city may be served by multiple zip codes, and a zip code may serve multiple cities.
The world's geography is not static; Yahoo! Placemaker acknowledges this reality. We employ a significant number of automated and editorial processes that are designed to ensure the currency and accuracy of our geographic resource. Constant administrative, postal, and geographic processes render locations obsolete: cities grow to absorb adjacent towns and villages, postal codes are created, terminated, and modified on a frequent basis in most countries that have them, and new development replaces outdated infrastructure. In Japan, for example, the "gappei" process constantly re-organises the nation’s official administrative geography by a method of merging, splitting, and redrawing geographical boundaries.
In cases where a place is stripped of its official status, Yahoo! will migrate the place to a historical category so that it can still be recognised, and its relationships to its successor places are updated so they can be discovered. Such places cease to be included in the administrative hierarchy. Their WOEIDs will remain unchanged.
In cases where a place is still current, yet has been redefined in respect of name, geometry or category, the WOEID will remain unchanged, and the attribution is updated to reflect the change.
As we continuously refine Yahoo! Placemaker there are times when we need to deprecate existing WOEIDs; there are two primary scenarios in which we will take this infrequent course of action:
For example, the place "CIA" was originally represented in Placemaker as a suburb category location, but subsequently identified as a match for "Calgary International Airport"; the original WOEID for the suburb place was thus deprecated and mapped to the new WOEID for the airport. Placemaker, however, continues to accommodate transparently and permanently the deprecated, duplicate WOEID. This approach to data management allows us to improve and refine the underlying resource without impacting offline content which has been indexed against it.
In the rare instance when this occurs, it is usually due to the integration of historical locations that have no bearing to the "real world", or situations where places are deemed to be unspecific or unverifiable.
In these situations, the WOEID of the invalid place will be deprecated and mapped to the WOEID of its parent place.
Yahoo! aims to capture the geography of the Earth as it is used by the world's people. To this end we are guided by various standards and sources of geographical information. For country codes and names, we rely on ISO 3166-1 but make no specific claim as to official designation or authority of disputed territories.
We appreciate that the subjective and personal nature of world geography ensures that there is no single authoritative hierarchy and we do not aim to impose one here. Rather, the Placemaker hierarchy is presented to facilitate geographic discovery, and ultimately assist in disambiguating identically named places, and resolving spatial appellations to a unique, open, and permanent identifier.
Yahoo! aims to improve Placemaker at every opportunity, and we could always use your help. Please post comments, questions, and bugs (outrageous!) to the Placemaker Forum.