8. A method performed by data processing apparatus, the method comprising: one or more computers configured to perform operations comprising: storing a respective plurality of category-location relevance scores for each location of a plurality of geographic locations, wherein each category-location relevance score for each location estimates a relevance of a respective category to the location, and wherein a category-location relevance score is based on a plurality of category-entity-location relevance scores for a plurality of entities associated with the category at the location, wherein storing a category-location relevance score for a location comprises storing a plurality of Taylor coefficients for a function at the location, wherein an evaluation of the function for a location provides a category-location relevance score for the category, and wherein an evaluation of the function at a location is determined by evaluating a sub-function for each of the plurality of entities, and wherein an evaluation of the sub-function for an entity provides a category-entity-location relevance score for the entity and the location; determining a first category-location relevance score for a first geographic location that is not one of the plurality of geographic locations, including: selecting a second geographic location in the plurality of geographic locations, and calculating the first category-location relevance score based on a second category-location relevance score for the second geographic location and a physical distance between the first geographic location and the second geographic location; and selecting an item from a plurality of candidate items using the first category location relevance score, wherein each candidate item is associated with a respective category, and wherein selecting the item comprises: ranking the plurality of candidate items using the first category location relevance score, and selecting a highest ranked candidate item.
8. A method performed by data processing apparatus, the method comprising: one or more computers configured to perform operations comprising: storing a respective plurality of category-location relevance scores for each location of a plurality of geographic locations, wherein each category-location relevance score for each location estimates a relevance of a respective category to the location, and wherein a category-location relevance score is based on a plurality of category-entity-location relevance scores for a plurality of entities associated with the category at the location, wherein storing a category-location relevance score for a location comprises storing a plurality of Taylor coefficients for a function at the location, wherein an evaluation of the function for a location provides a category-location relevance score for the category, and wherein an evaluation of the function at a location is determined by evaluating a sub-function for each of the plurality of entities, and wherein an evaluation of the sub-function for an entity provides a category-entity-location relevance score for the entity and the location; determining a first category-location relevance score for a first geographic location that is not one of the plurality of geographic locations, including: selecting a second geographic location in the plurality of geographic locations, and calculating the first category-location relevance score based on a second category-location relevance score for the second geographic location and a physical distance between the first geographic location and the second geographic location; and selecting an item from a plurality of candidate items using the first category location relevance score, wherein each candidate item is associated with a respective category, and wherein selecting the item comprises: ranking the plurality of candidate items using the first category location relevance score, and selecting a highest ranked candidate item. 14. The method of claim 8 , wherein approximating the first relevance score includes evaluating a Taylor series for the function using the Taylor coefficients for the function at the second geographic location and the physical distance between the first geographic location and the second geographic location.