During a discussion with my co-founder we started white-boarding the structure of the advertising industry. It turns out that its extremely complicated.
Let's try to break it down. Here is what it looks like if you want to advertise on general websites, blogs or mobile phone apps.
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That big crazy block in the middle is a network of large companies that each play a role in the ecosystem. Each block can represent a large company that excels at providing one component in the ecosystem. From the perspective of our favourite brand, Cowboy Binoculars, it is quite complicated, and they will usually employ an advertising agency to deal with it for them. The paths represent the different companies that you can choose from, and the colours represent many possible paths that could be taken.
However, this is not Cowboy Binoculars only option, they could also choose to advertise inside one of the walled gardens of the web. In this instance the structure looks abit more like the following diagram.
Here, we see that there are fewer companies to deal with, as the walled garden owner (Face-book, Google search, etc), controls the complete chain of ad delivery. Note that Cowboy Binoculars might still employ an ad agency, and that ad agency might use other companies, but once the ad is made it only deals with the large walled garden provider.