Ancestral DNA Affinity measures overall genetic distance across your whole genome compared to each ancient individual. It captures deep, population-level similarity and tends to surface ancient people whose overall profile — shaped by the same major ancestral layers — is closest to yours, even when you share no long recent segments.
Shared DNA Segments looks specifically for longer continuous stretches of identical DNA. Those are more likely to reflect actual shared recent ancestry (within the last few thousand years) or population-specific haplotype blocks that have stayed intact. Longer segments are rarer and tell you more about closer connections.
Together they give you two complementary views: affinity for deep population-level ancestry, and segment-sharing for closer or more specific connections.