Many other URLs redirect via their own URLs to better track which advertisements get clicked on. Of greater interest than the general consumer ads are the targeted ads. Rather than existing in general rotation or on very popular sites' home pages, a targeted ad is aiming at a specific audience. On the search engines, these are the advertisers that pay to have their ads displayed when a user searches a specific keyword or set of keywords. On other sites, a targeted ad may always be displayed on certain topic-specific pages of a site, or have a higher frequency of display in the rotation on that page.
Many sites displaying banner ads have a banner rotation program.
With banner rotation, any given page on a Web site rotates the banner ads. Instead of always displaying the ad for Joe's Garage on a specific page, the banner rotation script can present a different ad each time the page is visited. This rotation of ads creates some unusual difficulties in tracking advertising for competitive intelligence, market research, or even just for finding the ad you saw on the last page. Consequently, be careful when casually or quickly browsing the Web. It can be very difficult, due to banner rotation, to find the ad you saw yesterday or even on the previous page.