17. A system comprising: computer memory storing instructions that are executable; and one or more processing devices to execute the instructions to implement a keyword matching engine, an auction engine, and a geographic matching engine; the keyword matching engine to perform operations comprising: comparing words in an input query received from a computing device to keywords, the keywords being associated with content items that can be provided to computing devices; and generating, based on the comparing, matching scores indicating how well the input query matches keywords for different content items; the geographic matching engine to perform operations comprising: obtaining geographies associated with the computing device and associated with the content items that can be provided to computing devices; and identifying geographic matches between the computing device and at least some of the content items; the auction engine to perform operations comprising: including, in an auction, content items having matching scores that exceed a threshold and that match a geography of the computing device, the auction for receiving bids from content providers to determine which of the content items in the auction to output in response to the input query; the geographic matching engine to perform operations comprising: determining, based at least in part on bids provided in the auction, candidate content items for output in response to the input query; obtaining geographic areas associated with the candidate content items; and selecting a candidate content item having a smallest geographic area; and an output engine to perform operation comprising outputting the selected candidate content item in response to the input query.
17. A system comprising: computer memory storing instructions that are executable; and one or more processing devices to execute the instructions to implement a keyword matching engine, an auction engine, and a geographic matching engine; the keyword matching engine to perform operations comprising: comparing words in an input query received from a computing device to keywords, the keywords being associated with content items that can be provided to computing devices; and generating, based on the comparing, matching scores indicating how well the input query matches keywords for different content items; the geographic matching engine to perform operations comprising: obtaining geographies associated with the computing device and associated with the content items that can be provided to computing devices; and identifying geographic matches between the computing device and at least some of the content items; the auction engine to perform operations comprising: including, in an auction, content items having matching scores that exceed a threshold and that match a geography of the computing device, the auction for receiving bids from content providers to determine which of the content items in the auction to output in response to the input query; the geographic matching engine to perform operations comprising: determining, based at least in part on bids provided in the auction, candidate content items for output in response to the input query; obtaining geographic areas associated with the candidate content items; and selecting a candidate content item having a smallest geographic area; and an output engine to perform operation comprising outputting the selected candidate content item in response to the input query. 18. The system of claim 17 , wherein matching scores of the candidate content items are within a predefined tolerance of each other, and bids associated with the candidate content items are within a predefined tolerance of each other.