Dimensions and metrics

[GA4] Scopes of traffic-source dimensions

Traffic-source dimensions provide information about where your traffic originates from, the methods by which users arrive on your website or app, and the specific marketing efforts you use to drive that traffic. Learn more about traffic-source dimensions

Some traffic-source dimensions include the prefix "First user" (as in First user source) or "Session'' (as in Session source) to provide more attribution information. This article explains each prefix (or scope) and the type of information you can expect to see based on the scope.

In this article:

Traffic Sources in Google Analytics

Understand users, sessions, and events

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

  • User
    • Session
      • Event

A user is a person who interacts with your website or app. 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 visits 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 key 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, 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.

Learn more about reporting identity options in Google Analytics.

Understand scopes

Google Analytics organizes acquisition information into user, session, and event groups (or scopes) and adds prefixes to some dimensions so you can understand which groups the data applies to.

User-scoped dimensions

User-scoped dimensions show you where your new users are coming from. These dimensions always include the prefix "First user," as in the First user source dimension (which shows you the most common sources for new users). The value assigned to each user-scoped dimension remains the same as users return to your website or app.

Google Analytics surfaces information about user-scoped dimensions in the User acquisition report.

If the First user source dimension has a dimension value of "organic," for example, it means that these are users who landed on your website or app for the first time through an organic search (e.g., through Google Search).

When paired with a metric like Event count, the organic dimension value shows you the number of new users who landed on your website or app from an organic search (e.g., Google Search) and who triggered any event. For example, if you see 757,949 in the Event count column and the organic row (see the following table), then the new users who arrived through an organic search triggered 757,949 events in their first sessions.

If you were to change "Event count (All events)" to "Event count (add_to_cart)", then you would see the number of times new users, who arrived through an organic search, triggered the add_to_cart event in their first sessions.

First user medium +

Engagement rate

Event count

(All events)

Key events

(All events)

Total revenue

Totals 60.41% 2,681,227 69,325.00 $159,359.77
organic 68.25% 757,949 20,693.00 $32,042.15
cpc 51.22% 160,254 9,473.00 $2,933.50
referral 64.44% 161,321 4,372.00 $3,260.64

Session-scoped dimensions

Session-scoped dimensions show you where both new and returning users are coming from when they start new sessions. These dimensions always include the prefix "Session," as in the Session source dimension (which shows you the most common sources for new sessions). New values are assigned to session-scoped dimensions each time users return to your website or app.

Google Analytics surfaces information about session-scoped dimensions in the Traffic acquisition report.

If the Session source dimension has a dimension value of "organic," for example, it means that these are users who landed on your website or app through an organic search (e.g., through Google Search).

When paired with a metric like Event count, the organic dimension value shows you the number of new sessions that came from an organic search (e.g., Google Search) and in which users triggered any event. For example, if you see 888,666 in the Event count column and the organic row (see the following table), then the users who arrived through an organic search triggered 888,666 events.

If you were to change "Event count (All events)" to "Event count (add_to_cart)", then you would see the number of times users, who arrived through an organic search, triggered the add_to_cart event in their sessions.

Session medium +

Engagement rate

Event count

(All events)

Key events

(All events)

Total revenue

Totals 60.41% 2,681,227 69,325.00 $159,359.77
organic 67.33% 888,666 21,139.00 $55,912.49
cpc 52.22% 160,720 9,185.00 $2,294.65
referral 65.27% 231,175 4,530.00 $11,758.08

Event-scoped dimensions

Event-scoped dimensions help you attribute credit for a key event that a user triggered. Event-scoped dimensions don't include a prefix, as in Source or Medium. The source and medium for non-key events are "(not set)".

Google Analytics surfaces information about event-scoped dimensions in the Model comparison and Key event paths reports. For example, the following table illustrates what you might see in the Model comparison report, which shows various metrics for each value of the Medium dimension:

  Google paid channels last click model Google paid channels data-driven model
Medium + Key events Revenue Key events Revenue
Totals 69,325.00 $159,359.77 69,325.00 $159,359.77
organic 20,139 $52,932.49 20,136.78 $52,932.49
cpc 9,135 $2,134.66 9,138.93 $2,134.66
referral 4,392 $11,358.19 4,382.29 $11,358.19

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 paid and organic channels last click attribution model. User-scoped and session-scoped dimensions are unaffected by changes to the attribution model.

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.

Example

Debra, an online retailer, sets up Google Analytics to see how users find her ecommerce website. The following describes one customer's path through the ecommerce website and how Debra can use the reports in Analytics to understand the customer's journey.

Initial sessions

Sam is a customer of the ecommerce website. He discovers the website through an unpaid Google Search result. Sam clicks the search result, lands on the ecommerce website, views some of the products, and then signs up for the newsletter. A few days later, Sam clicks a link in an email marketing campaign, returns to the website, and completes a purchase.

The following illustrates Sam's path:

User: Sam

Session 1: Unpaid search → first_visit (key event) → session_start → view_item → signup

Session 2: Email marketing → session_start → purchase (key event)

More 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:

User: Sam

Session 3: Paid search → session_start → Affiliate with UTM parameters → view_item → add_to_cart (key event)

Session 4: (none) → session_start → purchase (key event)

Results

Debra, the store owner, see the following results in Google Analytics:

User-scoped dimensions

First user source / medium is assigned at the user level and represents the source / medium that acquired the user in the first session.

User First user source / medium
Sam (user) google / organic

Session-scoped dimensions

Session source / medium is assigned at the session level and represents what originated the session. Sessions initiated by direct entrance are attributed to the last known source/medium for that user.

Session Session source / medium
Session 1 google / organic
Session 2 email / newsletter
Session 3 google / cpc
Session 4 partner / affiliate

Event-scoped dimensions

The following table shows the number of key events for each event triggered in the previous examples. The table includes the key event paths that the user took to trigger each key event. While the view_item event was triggered twice, the event is not marked as a key event so it doesn't have a key event path.

The key event count and key event paths are defined as follows:

Event name Event count Key events Key event paths
first_visit 1 1 google / organic
purchase 2 2

google / organic > email / newsletter

google / organic > email / newsletter > google / cpc > partner / affiliate

add_to_cart 1 1 google / organic > email / newsletter > google / cpc > partner / affiliate
view_item 2 0 -

Then, Analytics attributes credit to each source / medium according to the attribution model that you selected in the property settings. In this example, we used the default data-driven attribution model. The attribution for source / medium only applies to events marked as key event:

Source / medium Key events
google / organic 1.3
email / newsletter 1.1
google / cpc 0.6
partner / affiliate 1
direct / (none) 0

Note: Google Analytics puts different weights on each touch point along a user's path to key event. These numbers are illustrative and don't necessarily represent the exact weights that Google puts on each touchpoint.

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