IDFA / GAID

IDFA (Identifier for Advertisers) on iOS and GAID (Google Advertising ID) on Android are resettable device identifiers used for ad measurement and targeting. They allow MMPs to match ad interactions to installs and let advertisers build audiences for retargeting.

Since Apple's App Tracking Transparency, apps must ask permission before accessing the IDFA, and many users decline. As a result, most iOS attribution now relies on SKAdNetwork. On Android, GAID remains available where users have not opted out, though Google's Privacy Sandbox is changing how it works. UA strategies therefore treat iOS and Android separately, with different measurement setups and expectations.

For advertisers, the practical consequences are smaller retargeting audiences on iOS, more reliance on aggregated measurement and greater importance of contextual signals such as app, placement and time when bidding. Planning for these limits from the start avoids unpleasant surprises later.