This article is about Google Analytics 4 properties. Refer to the Universal Analytics section if you're still using a Universal Analytics property, which will stop processing data on July 1, 2023 (October 1, 2023 for Analytics 360 properties).

[GA4] Scopes of traffic-source dimensions

See where new users and sessions are coming from

Traffic-source dimensions are dimensions that describe where your users come from. The dimensions include the prefix "First user" or "Session" (as in First user source or Session source) to distinguish information about new users and sessions from information about triggered conversion events. Learn more about dimensions

This article explains each prefix (or scope) and the type of information you can expect to see based on the scope.

In this article:

Understand users, sessions, and events

Google Analytics organizes users, sessions, and events in the following hierarchy:

  • User
    • Session
      • Event

A user is an individual who interacts with your business. If two different people interact with your website, for example, then Google Analytics considers each person to be a separate user. If someone leaves your website and comes back later, for example, then Google Analytics still considers them to be one user. Learn more about users

A session is the period from when a user visits your website or app to when they leave your website or app. For example, someone visits your website, adds something to their shopping cart, and then leaves your website. The next day, they return to your website and purchase something. These separate interactions are two separate sessions. Learn more about sessions

An event is a distinct user interaction within a session. In the previous example, adding something to a shopping cart, leaving an ecommerce store, and purchasing something are all examples of interactions that you can measure using events. You can mark the events that are most important to your business as conversion events. Learn more about events

How Google Analytics identifies a user

Google Analytics identifies an individual user based on the reporting identity option you choose for your property and the user's browser or device settings.

For example, if you choose the blended reporting identity for your property, then Analytics will factor in the user ID, device ID, Google signals, and modeling to identify the user. If any of these identities are the same (e.g., the user has the same user ID across sessions), Google Analytics will identify the individual as the same user.

To learn more about the reporting identity options in Google Analytics, see Reporting identity.

Understand scopes

Google Analytics organizes acquisition information into user, session, and event buckets and adds prefixes to some dimensions so you can understand which buckets they apply to. The buckets are user-scoped, session-scoped, and event-scoped.

User-scoped dimensions

User-scoped dimensions describe where new users come from. User-scoped dimensions have the prefix "First user" as in First user source. If a user returns to your website more than once, their user-scoped dimension doesn't change.

Example
 
You can see the channel groupings that generate the most new users by looking at the First user default channel grouping dimension. If someone visits your website in January and then again in April, the value assigned to the dimension for the user in April will be the same value assigned in January.

Google Analytics surfaces information about user-scoped dimensions in the User acquisition report. For example, the following shows various metrics for the First user medium dimension. The Event count and Conversions columns show the events that users trigger in their initial session. You can choose events to see the First user medium for the user's initial session in which they triggered the event.

Session-scoped dimensions

Session-scoped dimensions describe where new sessions come from, regardless of whether the user is new or returning. Session-scoped dimensions have the prefix "Session" as in Session source. If a user returns to your website more than once, their session-scoped dimension changes to describe where the user came from to begin the session.

Example
 
You can see the channel groupings that generate the most new sessions by looking at the Session user default channel grouping dimension. If someone visits your website in January and then again in April, the value assigned to the dimension for the user in April will be different from the one assigned in January.

Google Analytics surfaces information about session-scoped dimensions in the Traffic acquisition report. For example, the following shows various metrics for the Session medium dimension. The Event count and Conversions columns show the events that users trigger in each session. You can choose events to see the First user medium for a user's session in which they triggered the event.

Event-scoped dimensions

Event-scoped dimensions describe the session in which the user triggered a conversion event. Event-scoped dimensions don't have a prefix as in Source. The source and medium for non-conversion events are "(not set)". Learn more about conversion events

Example
 
You can see the channel groupings that generate the most triggered conversion events by looking at the Default channel grouping dimension. If someone visits your website in January and then again in April to purchase a product, the value assigned to the dimension will be about how you acquired the user when they made the purchase.

How Analytics attributes credit

Analytics uses different attribution models to assign credit to the ads, clicks, and other interactions along a user's path that leads the user to your website or app.

For user-scoped and session-scoped dimensions, Analytics uses the cross-channel last click attribution model. User-scoped and session-scoped dimensions are unaffected by changes to the attribution model. Learn more about attribution models

For event-scoped dimensions, Analytics uses the attribution model that you select, but by default, Analytics uses the data-driven attribution model. All reports with event-scoped traffic dimensions reflect the attribution model you select. Learn more about selecting an attribution model

Example

An online retailer sets up Google Analytics to see how users find her ecommerce website.

Initial sessions

Sam is a customer of the ecommerce website who finds the website through an ad on YouTube. After Sam views the YouTube ad, he visits the ecommerce website, views some of the products, and then signs up for the newsletter. A few days later, Sam clicks a shopping ad, returns to the website, and completes a purchase.

The following illustrates Sam's path:

Follow-up sessions

One week later, Sam clicks an ad on Google Search, views a product, adds the product to his shopping cart, and then bookmarks the product page. In the middle of the third session, Sam clicks a link to view the product, which has a UTM parameter of utm_source=
"internal_promotion"
. Later in the week, Sam uses the bookmark to open the product page, goes to the shopping cart, and purchases the product.

The following illustrates Sam's path:

Results

The store owner leaves the attribution settings as the data-driven attribution model. The owner will see the following results:

Session First user source / medium Session source / medium Source / medium
Session 1 youtube / cpc youtube / cpc youtube / cpc
Session 2 youtube / cpc google / cpc google / cpc and youtube / cpc
Session 3 youtube / cpc google / cpc google / cpc and youtube / cpc
Session 4 youtube / cpc (direct) / (none) google / cpc, youtube / cpc, and (direct) / (none)
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