1. A computer-implemented method comprising: identifying, by a system of one or more computers, a portion of a geographic map for presentation on an electronic display of a computing device; identifying, by the system, a set of content items that are candidates for presentation on the portion of the geographic map and that are each associated with a respective geographic location that is located within a geographic area represented by the portion of the geographic map; identifying, by the system, a distance between a first geographic location that is associated with a first content item of the set of content items and a second geographic location that is associated with a second content item of the set of content items; determining, by the system and based at least on the distance between the first geographic location that is associated with the first content item and the second geographic location that is associated with the second content item, whether to present the first content item on the electronic display of the computing device along with the portion of the geographic map; and in response to determining to present the first content item on the computing device along with the portion of the geographic map, providing, by the system, over a network and to the computing device, data that instructs the computing device to present the first content item along with the portion of the geographic map.