8. A machine-implemented method, the method comprising; presenting, using one or more computing devices, a user interface for a campaign sponsor for customizing targeting information for a campaign including a search control for discovering areas for targeting; receiving, using the one or more computing devices, user input in the search control including a textual description of an area to target; providing, using the one or more computing devices: one or more results that satisfy the textual description, estimated reach information for each result, each result representative of a geographic feature that can be targeted in the campaign, wherein the estimated reach information for each result indicates a number of unique users to be targeted within a geographic feature associated with the result, and a limited reach indicator based on a confidence level related to available estimated reach information; providing with each result, using the one or more computing devices: an add control that, when selected, adds a geographic feature associated with the result to the campaign, and an exclude control that, when selected, excludes a geographic feature associated with the result from the campaign; receiving, using the one or more computing devices, for at least one of the one or more results, user input to select one of the add control or the exclude control corresponding to the at least one of the one or more results; and adding, using the one or more computing devices, the geographic area to the campaign or excluding the geographic area from the campaign based on the selection.
8. A machine-implemented method, the method comprising; presenting, using one or more computing devices, a user interface for a campaign sponsor for customizing targeting information for a campaign including a search control for discovering areas for targeting; receiving, using the one or more computing devices, user input in the search control including a textual description of an area to target; providing, using the one or more computing devices: one or more results that satisfy the textual description, estimated reach information for each result, each result representative of a geographic feature that can be targeted in the campaign, wherein the estimated reach information for each result indicates a number of unique users to be targeted within a geographic feature associated with the result, and a limited reach indicator based on a confidence level related to available estimated reach information; providing with each result, using the one or more computing devices: an add control that, when selected, adds a geographic feature associated with the result to the campaign, and an exclude control that, when selected, excludes a geographic feature associated with the result from the campaign; receiving, using the one or more computing devices, for at least one of the one or more results, user input to select one of the add control or the exclude control corresponding to the at least one of the one or more results; and adding, using the one or more computing devices, the geographic area to the campaign or excluding the geographic area from the campaign based on the selection. 12. The method of claim 8 , wherein the limited reach indicator is provided if the confidence level is below a predetermined threshold.