1. A computer-implemented method, the method comprising: receiving a targeting request that identifies a target geographic region; identifying one or more groups of geographic regions that each include at least two geographic regions, including the target geographic region, wherein the one or more groups of geographic regions are identified based on respective combined targeting accuracies, the respective combined targeting accuracy of each of the one or more groups being higher than a targeting accuracy for the target geographic region; and providing data describing the identified one or more groups of geographic regions in response to the targeting request.