List of advertising data exchanges and aggregators online. Data aggregators are online systems allowing advertisers to quickly gather a lot of information about their online ads and the users who are seeing them, including geographic, demographic, lifestyle, purchase history and occupational background. Most aggregators ultimately aim to minimize the amount of waste and detect ads that are proving ineffective, while also analyzing the placement of advertisements around websites or ad networks and measuring the level of user engagement. This in turn helps the advertiser decide whether or not it is profitable to continue funding the advertisement or campaign. Some of the data exchanges and aggregators included on this list are BlueKai, Exelate and RapLeaf.