Yahoo! GeoPlanet uses a hierarchical model for places that provides both vertical consistency and horizontal consistency of place geography. The model ensures that places in each layer in the hierarchy overlay the correct and corresponding places in other layers, and that geographical relationships are preserved. The hierarchy allows developers to query the geographic context of every named place represented by a WOEID.
Every place belongs to a number of containing, superior (larger) geographic entities, and in turn may contain a number of inferior (smaller) geographic entities. The smallest fully containing official geographical entity for a place is called its parent. The list of containing official geographic entities for a place is called its ancestors. The fully contained geographic entities for a place are called its children.
The hierarchy recognizes a distinction between "official" administrative places, such as country, state, county, & city, and "informal" places, such as colloquial places and historical administrative places. These unofficial places are included in a separate collection called belongtos.
A place can have both official and informal children. Consider three examples:
A Point of Interest (POI) place type whose 'parent' is North End (neighbourhood), its 'Ancestors' are North End, Boston (town), Suffolk (county), Massachusetts (state), US (country) and of course, the Earth (you are here).
Additionally it 'belongsto' 02114 (zipcode), 617 + 857 (area codes), Boston-Cambridge-Quincy (Metro Statistical Area), New England (colloquial), America/New York (Timezone), and North America (continent)
A colloquial place type whose 'parent' is California (state), its 'ancestors' are California (state), US (country), and Earth, while its 'children' include Alameda, Contra Costa, Marin, Napa, San Francisco, San Mateo, Santa Clara, Solano, Sonoma (counties)
Additional children include all of the GeoPlanet entities (Towns, Neighborhoods, Points of Interest, Airports) that have these 9 counties as ancestors.
A postal code place type, is found in three countries: United States, Germany, Mexico. The US place has 'parent' Sunnyvale (town), and 'ancestors' Sunnyvale (town), Santa Clara (county), California (state), US (country), and the Earth.
Additionally it 'belongsto' 408 (area code), San Jose-Sunnyvale-Santa Clara (MSA), San Francisco Bay Area (colloquial), Silicon Valley (colloquials), America/Los Angeles (Timezone), and North America (continent).