Walled gardens represent areas in the digital media space where paid media can be purchased, but limited or no tracking data can be extracted at the event level. Most walled gardens will certainly ingest advertiser data in order to optimize campaign performance within the walls of their walled garden, but often do not provide granular (or any) data back to advertiser to allow them to optimize throughout their initiative (across both walled garden and other publishers). The social channels are probably the most famous of the Walled Gardens, including Google YouTube, Facebook, Instagram, Twitter and others.
Walled gardens present a particularly large and existential challenge for marketers and other players within the digital media space since most media dollars are actually captured by the walled gardens
