Underdelivery of geo-targeted line items
Line items targeted to geographic criteria can underdeliver, or appear to underdeliver, in the following circumstances:
Users didnt match the geographic criteria set for the line item: Due to the dynamic nature of the web, there is no guarantee that a user located in a given postal code will access the web while your line item campaign is running. Furthermore, the line item servers can select any line item to deliver to a user who matches the targeted criteria of the line item that you booked. For example, if a line item is behind schedule, it can be served to the user even if other line items are targeted specifically to their postal code.
DFP doesn't recognize the IP address of the user: IP addresses are used to collect information for geographic targeting. For some line item requests, geographic data may not be available because the user's outward-facing IP address is actually the IP address of a proxy server. For other line item requests, the country of origin can't be determined because the servers are not registered with third-party sources and don't use country-specific IP addresses. In other cases, it might be possible to identify the user's country, but not more specific geographic information.
If DFP doesn't recognize the IP address at all, then line items targeted to criteria based on IP address are not served (but other line items can still be served).
The IP address of the user is mapped to the wrong geographic location: Geographic information can change. For example, countries can add new area codes or change the coverage of existing codes. To maintain accurate area code targeting, DFP must map the new area codes to their physical location, and updated the existing mapping for area codes to reflect the areas the codes now cover.