Geographic information for targeting is derived either through IP geolocation and lat/long information. The overall accuracy of geotargeting varies. Basis DSP uses the best information available for targeting: we automatically use lat/long when available and use IP geolocation otherwise.
IP geolocation is used for all desktop. IP information is based on registration data about the owner of an IP address (i.e. the ISP) and triangulation. This data is accurate at the country level (99%+), but not as accurate at the city level (80%+). VPNs and proxy servers may cause a user to appear to be somewhere significantly different than their actual location; they will appear to be at wherever the VPN or proxy server is located. The IAB states that IP targeting is generally 88% accurate to within 25 miles, and depending on how targeted you are getting, that number decreases – the smaller the range, the lower the accuracy. For example, targeting specific postal codes or zip codes is not recommended when precision is necessary as accuracy is poor at this level. The results are directionally useful, but can not be expected to be perfect. MaxMind, our IP geolocation provider, describes their data to be reliable to the exact postal/ZIP code 40% of the time in US, and 33% of the time in Canada.
For mobile, IP geolocation is somewhat unreliable. Mobile carriers tend to route all of their Internet traffic over their own internal networks and out to the public Internet at a handful of points. Basis DSP uses latitude and longitude from the bid request wherever possible. This lat/long is usually derived from the GPS unit in the phone, wi-fi triangulation, or registration data (in apps where users register). Accuracy varies depending on data type: GPS provides <100m resolution, Wi-fi data provides <500m resolution, and registration data is generally accurate to the user’s home address.
Below are a couple of useful links from the IAB that outline these issues:
(Accuracy data from our IP geolocation provider)