What is the difference between an opportunity to see and an impression?
An opportunity to see (OTS) is a qualified type of impression, defined by the conditions attached to it 12. In out-of-home and in-store measurement, an ad impression is the potential exposure by an individual to a particular advertising content play, calculated as audience multiplied by ad play 13. OTS narrows that count by adding viewability requirements 1.
How the impression funnel is layered
At the top of the funnel is the gross impression, which requires an ad play, a functional display, and presence in the exposure zone 1. OTS impressions, also called viewable impressions, count exposures with presence in the defined display exposure zone while the display is functional and a viewability condition exists 2. For out-of-home, the cross-media requirement applied is 100% of pixels on-screen for one second for display and static, and 2 continuous seconds for video 2. Logical obstructions negate the counting of viewable ad impressions 2.
What opportunity to see does not tell you
OTS counts everyone who passes within the exposure zone of a screen, representing potential exposure without confirming actual viewership 1. Viewing should be understood as the opportunity to look at the screen when an ad was confirmed as played for someone in front of that screen 1. A further layer, likelihood to see (LTS), applies an adjustment for the likelihood of exposure with some evidence of notice or seen 12.
Why the distinction matters in store
IAB Europe describes opportunity to see as the best proxy available for a viewable ad impression in the in-store environment 3. The word "opportunity" carries the qualification: entering a store gave a person the chance to see the advert 13.