Understand the Ad Selection Process

Ad selection refers to the process of how Google Ad Manager chooses the best ad to serve to users. Understanding this process will help you with troubleshooting ad delivery.

Behind the scenes of the ad selection process

Let’s start with an overview of the ad selection process. 

First, the browser or app requests an ad from the ad server. Next, the ad server gathers information from the ad request. Then a list of eligible line items is created and Ad Manager selects the best one. Finally, Ad Manager selects the best creative associated with the winning line item and returns it to the browser or app. 

There’s a lot going on behind the scenes that helps Ad Manager serve the best ad. Let’s walk through the process, step by step. We’ll start with the request. 

The ad selection process begins when an ad request reaches the Ad Manager ad server. The initial request sends quite a bit of information, such as details in the ad tag, including the ad unit, size of the ad slot, key values, the IP address, HTTP header, and user identifier, which contains no personally identifiable information. Mobile device capabilities may also be attached to the request. 

So what does this mean? Well, from this ad request, Ad Manager knows the ad unit path, requested ad sizes, and that there’s no additional key value targeting. From the IP address, Ad Manager knows that the user is located in London. From the HTTP header, Ad Manager knows that the user is viewing the site on a Chromebook. 

In addition, by looking at identifiers in the request, we know that the user has previously visited the page or requested an ad. 

In terms of ad selection, the targeting and settings for each line item acts as a checklist that Ad Manager compares against the information from the tag. This allows Ad Manager to determine which line items are eligible to serve to the user. Once Ad Manager has this information, a list of eligible line items is compiled. 

Ad Manager then eliminates any line items that are ahead of schedule, not eligible to serve at this time of day, have met their frequency cap, as well as the ones subject to competitive and ad exclusion restrictions. 

In this example, there were four line items to be evaluated for eligibility. Let’s take a look. 

YourAdventure’s Sail Away campaign meets all the criteria except that the frequency cap for this line item has been met. It will drop from the list. 

The next line item, YourAdventure’s Global Getaway 300×250 campaign will be dropped because its day-part targeting has been applied for another time period. 

The next two line items match the criteria exactly. So they move on to the next step of the ad selection process. 

Ad Manager ranks line items by priority level. For example, this request returned one eligible standard and one eligible network line item. When ranked by priority, this standard line item, “YourAdventure Luggage Campaign” would take precedence since it has a higher priority than the network line item “YourAdventure Travel by Train.” 

In some cases, Ad Manager might have several line items eligible at the same priority, but with different goal types. When this happens, Ad Manager will then prioritize by goal type (percentage-based, impression-based, and unlimited). 

This means if the list of eligible ads includes a network, bulk, and price priority type, Ad Manager would select them in this order: network, bulk, price priority. 

If AdSense or Ad Exchange is not enabled for your network or not eligible for this ad request, Ad Manager will select the winning line item, then check the Adjust Delivery, Display, and Rotate Creative settings to select the right creative (if more than one creative is associated with the line item). Then that creative is served. 

However, if your network does have AdSense or Ad Exchange enabled, there is more to this process. Ad Manager gives you the option to connect to your AdSense or Ad Exchange accounts, allowing you to monetize your network’s unfilled inventory. 

If an AdSense or Ad Exchange line item is eligible for an impression, that line item and all eligible non-guaranteed line items are compared with guaranteed line items using a process called dynamic allocation. 

Ad Manager selects the best eligible line item. However, instead of selecting the best creative and returning it to the browser or app, Ad Manager ranks all eligible non-guaranteed and AdSense or Ad Exchange line items by their value CPM. Ad Manager chooses the highest value non-guaranteed line item to compete with the temporary CPM calculated for guaranteed line items.

At the end of the dynamic allocation process, Ad Manager will have the winning line item chosen based on which has the highest CPM. If AdSense or Ad Exchange has the highest CPM, it will be chosen and served. 

If the winning line item is not AdSense or Ad Exchange and has multiple creatives associated with it, Ad Manager checks the Display and Rotate Creative settings to determine the correct creative to display.

Lastly, Ad Manager returns the best creative associated with the winning line item to the browser. 

Some final important things to note: 

If you have multiple AdSense or Ad Exchange line items with overlapping targeting, then only one will be eligible to compete in dynamic allocation. 

If identical priority levels are set for AdSense or Ad Exchange line items, then Google Ad Manager will pick one at random to compete. This may not be an optimized delivery yield. 

Remember that dynamic allocation allows you to optimize your delivery on yield, increasing your revenue without compromising your directly sold, guaranteed campaigns.