As advertisers collect data across multiple external websites about a user's online activity, they can create a detailed picture of the user's interests to deliver even more targeted advertising. This aggregation of data is called behavioral targeting. Advertisers can also target their audience by using contextual and semantic advertising to deliver display ads related to the content of the web page where the ads appear. Retargeting, behavioral targeting, and contextual advertising all are designed to increase an advertiser's return on investment, or ROI, over untargeted ads.
Advertisers may also deliver ads based on a user's suspected geography through geotargeting. A user's IP address communicates some geographic information (at minimum, the user's country or general region). The geographic information from an IP can be supplemented and refined with other proxies or information to narrow the range of possible locations. For example, with mobile devices, advertisers can sometimes use a phone's GPS receiver or the location of nearby mobile towers.Cookies and other persistent data on a user's machine may provide help narrowing a user's location further.