The document discusses the limitations of the "last ad" model for measuring digital advertising ROI and introduces engagement mapping as a new standard. The "last ad" model only credits the final ad interaction before a conversion, ignoring all previous touchpoints. This misaligns with conventional marketing concepts like awareness building across the sales funnel. New research shows the importance of understanding interaction between channels, as overlap drives higher conversion rates. Engagement mapping counts every customer touchpoint and better enables advertisers to effectively target audiences across the entire customer journey.