Dimensions Sources in BQ/GA4: Distinction between "User Sources" and "Session Sources

👋 In this document, you'll discover the difference between the different acquisition levels, as well as the distinctions between GA4 and BigQuery.

1 - Understanding the concept of session and acquisition in GA4

Session structure in GA4

Each user visiting a website can generate one or more sessions. During each session, this user can perform one or more actions, called events.

There are three levels of analysis in GA4:

• The user level: which groups together all the interactions of an identified individual.
• Session level: corresponds to a visit, from start to finish.
• Event level: every action performed during a session (click, scroll, add to cart, etc.).
  

The notion of acquisition

Acquisition represents the origin of traffic to your site. In other words, the channel or source that brought a user to your site.

This notion can be found on three levels:

• User level the very first source of acquisition (eg: first user source).
• Session level the source that generated each session (eg: session source).
• Event level: the source at the moment an event is triggered.

💡 A user may arrive on your site from channel A, leave, then return within 30 minutes via channel B. In this case, GA4 considers a single session to be in progress, unlike GA3, which counted a new session each time a channel was changed.

2 - Acquisition dimensions in GA4

In the GA4 interface, there are two main types of acquisition dimensions:

• User level : first user source, first user medium, first user campaign
  → This is the first source that brought the user to the site.

• Session level : session source, session medium, session campaign
  → This is the last non-direct source of the current session.

These dimensions are available in the reports :

• User Acquisition
• Traffic Acquisition

In the GA4 explorer, you can also access the event levelthrough source, medium, campaign at the time of each action.

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Case in point:‍

• first user source = Facebook
• session source = Google Ads

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3 - Acquisition dimensions in BigQuery

With BigQuery, data is more granular and allows for finer analysis:

• User level: the first source detected for the user.
• Session level the last non-direct source of the session, with several variants:
  • manual: data from UTM parameters
  • Google Ads: detailed data on the Google ads campaign if the source is Google Ads
  • cross-channel: acquisition sources reprocessed by Google with the model used on GA4.
  • SA 360 / CM 360 / DV 360: platform-specific data (if used)
• Event level: UTM parameters captured at each event.

Which size to use?

If you work with BigQuery :

As part of an acquisition project using Bigquery data, we will follow the steps below:

1. Scoping workshop: a workshop with the customer to understand real acquisition needs.
2. Modeling: the construction of an attribution model adapted to the expressed and identified need.

In the absence of specific needs :

If you're building a dashboard on Looker Studio and have no special needs for the acquisition part, we recommend using :

cross-channel last click ,  this is the closest to standard GA4 ratios. : session_traffic_source_last_click.cross_channel_campaign.