One of the key strengths of digital advertising is that it can provide detailed metrics on how advertising campaigns are performing. The most fundamental metrics are impressions (the number of times an ad has been served) and clicks. Here are some insights into exactly how DFP counts those metrics.
Counting impressions
In general, DFP counts an impression each time a creative is sent to an end user. By that stage in the process, we've already read the user's DoubleClick cookie, if available, and completed the process of choosing which ad and creative to serve. Note that the impression is counted before the creative is fully downloaded and viewed by the end user.
Delayed impressions
Some ad types use delayed impressions. In these cases, the initial creative code is delivered to the end user in advance, but the impression isn't counted until DFP receives a followup request for the creative asset itself.
Delayed impressions are used with:
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Prefetched ads
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Out-of-page ads
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Video ads
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Mobile ads
Counting clicks
When a user clicks on an ad, a request is sent to the DFP ad servers. As soon as DFP receives the request, it counts the click. DFP then sends the user the redirect URL, which takes the user to the landing page. Note that DFP counts the click when it's received, not when the user is sent the redirect URL.
Discarded impressions and clicks
DFP discards impressions and clicks that are considered invalid. These are impressions and clicks that are not generated by actual people browsing the web, or that are accidentally generated. Invalid impressions and clicks can come from a variety of sources, including:
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Web crawlers and spiders, which are programs that systematically load webpages and click on links in order to gather data
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Impressions and clicks from sources that we've determined are not legitimate
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Inadvertent double-clicks on ads, which are counted as a single click