Identifying Unique Visitors

Last update: June 9, 2021

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The method for identifying unique visitors among multiple contexts includes a prioritized sequence to ensure accuracy in this determination. The following table shows this prioritized sequence:

Order usedQuery parameter (collection method)post_visid_type column valuePresent when
1vid s.visitorID0s.visitorID is set.
2aid  s_vi cookie3Visitor had an existing s_vi cookie before you deployed the Visitor ID service, or you have a Visitor ID grace period configured.
3mid AMCV_ cookie set by Identity Service5Visitor’s browser accepts cookies (first-party), and the Identity Service is deployed.
4fid fallback cookie on H.25.3 or newer, or AppMeasurement for JavaScript4Visitor’s browser accepts cookies (first-party).
5HTTP Mobile Subscriber header2Device is recognized as a mobile device.
6IP Address, User Agent, Gateway IP Address1Visitor’s browser does not accept cookies.

For information on how unique visitors are reported, see Unique Visitors in Analytics.

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