Source / medium: the core traffic-origin dimension
Source/medium is the dimension that records where a visit came from (the source, e.g. google) and how it arrived (the medium, e.g. organic). It is derived from the referrer and UTM parameters, with rules that vary by tool. The big caveat: when neither is available, the visit lands in 'direct / (none)', which is a catch-all, not a channel.
What this means
Source is the origin (google, newsletter, a domain); medium is the channel type (organic, cpc, email, referral). Tools combine them into 'source / medium'. UTM parameters set them explicitly; otherwise the tool infers them from the referrer.
How it is derived and where it breaks
UTM tags win over the referrer. With no UTM and no usable referrer, the visit is 'direct / (none)'. That bucket fills up from app and messaging opens, stripped referrers, and untagged campaigns — so a big 'direct' share is usually lost attribution, not loyalty.
- utm_source / utm_medium override the referrer
- No referrer + no UTM => direct / (none)
- Channel grouping rolls source/medium into channels
How it appears in analytics and logs
A source/medium value is the tool's best guess at origin from referrer + campaign tags. A large 'direct / (none)' share usually means missing referrers or untagged campaigns, not type-in loyalty.
Diagnostic use case
Read source/medium to attribute traffic to origins, while knowing UTM tags override referrer and that 'direct' absorbs anything unattributable.
What WebmasterID can help detect
WebmasterID attributes visits from referrer + utm_* at ingest and keeps 'direct' honest rather than guessing, so the dimension reflects what is actually known.
Common mistakes
- Reading 'direct / (none)' as type-in/brand traffic.
- Forgetting UTM tags override the referrer.
- Comparing channel grouping rules across tools as if identical.
Privacy and accuracy notes
Source/medium derives from the referrer header and URL parameters, not from cross-site identity. WebmasterID reads them first-party and never fingerprints to fill gaps.
Related pages
- Device category: desktop, mobile, tablet
Device category groups visits into desktop, mobile, or tablet. It is derived from the user-agent string (increasingly, User-Agent Client Hints), so it is a classification, not a hardware fact. Tablets, desktop-mode mobile browsers, and foldables blur the boundaries, and the user agent can be spoofed.
- Direct traffic: what it really means
Direct traffic is the bucket analytics uses when no referrer is available. It includes genuine type-ins and bookmarks, but also a large share of visits whose referrer was stripped — app opens, HTTPS-to-HTTP transitions, shorteners, and privacy settings. Treating 'direct' as a single intent is the classic analytics mistake.
- UTM parameters explained: the five tags and how to use them
UTM parameters are query-string tags you add to a link so analytics can attribute the visit to a campaign even when the referrer is missing. This page explains the five tags, a consistent naming convention, and the hard rule that UTM values are public — so they must never contain personal data or secrets.
- Attribution analytics
Directional attribution across AI, search, and referral traffic.
Sources and verification notes
Last reviewed 2026-06-24. Facts are checked against primary/official sources where available; uncertain specifics are marked “Data not yet verified” rather than guessed.