9. A system comprising: one or more computers and one or more storage devices storing instructions that are operable, when executed by the one or more computers, to cause the one or more computers to perform operations comprising: receiving a query that includes a first geographic entity name; identifying a candidate substitute term for the first geographic entity name, wherein the candidate substitute term is a second geographic entity name; determining that the geographic entity name and the second geographic entity name have a particular relationship in a geographic data set that includes a plurality of names of geographic entities and respective relationships between pairs of geographic entities; obtaining search results that satisfy the query; and demoting a score of an obtained search result that corresponds to a document that includes the second geographic entity name based at least in part on the determined particular relationship between the first geographic entity and the second geographic entity.
12. The system of claim 9 , wherein the geographic data set is a tree structure wherein different positions in the tree structure that share a same level correspond to different geographic locations that share a same geographic region type.