GA4 Users, Sessions, Events, and Key Events in a Community Context

The GA4 Data Hierarchy

Google Analytics 4 is built on an "event-based" model. This means that nearly every piece of data it collects is an event—an interaction between a user and your website or app. These events are then grouped into sessions (visits), which are in turn attributed to users (the people visiting).

This creates a simple hierarchy:

• Users have...
• Sessions, which contain...
• Events

Let's break down each of these components, starting from the most fundamental unit: the event.

Events: The Foundation of Measurement

In GA4, an event is any distinct user action that you want to measure. It could be as simple as viewing a page or as specific as submitting a comment on a forum post.

To get a formal definition, let's turn to Google's official documentation.

Not all events are created equal. GA4 groups them into four categories, which is important to understand because it determines how much setup work is required.

As the video explained, the four types are:

1. Automatically collected events: These are tracked by default once you install GA4 (e.g., session_start, page_view, first_visit).
2. Enhanced measurement events: These are also automatic if you enable the feature. They track common web interactions like scrolls (scroll), outbound clicks (click), and file downloads (file_download).
3. Recommended events: These are not automatic, but Google provides a predefined list of names and structures for common scenarios (e.g., sign_up, login, post_score). Using these helps GA4 understand your data better.
4. Custom events: If no existing event type fits your needs, you can create your own from scratch. For our community, an event like attended_virtual_meetup would likely be a custom event.

Key Events: Marking What Matters

Your GA4 property will collect hundreds of thousands of events. Most of them are just "noise" in the context of your core goals. This is where Key Events come in. A Key Event is simply an event that you have marked as being critically important to your business. In previous versions of Google Analytics, these were called "conversions."

Let's go back to the Google Help article to see the official definition.

Let's connect this to our community framework from the last lesson:

• Acquisition: A new member signing up would trigger a sign_up event. We would mark this as a Key Event to measure acquisition.
• Activation: A new member making their first post might trigger a post_comment event. We could mark this as a Key Event to measure our "aha!" moment.

By marking these events, you tell GA4, "Pay special attention to these actions." This makes them easier to analyze and enables certain features in the platform.

Sessions: Grouping Events into Visits

A single event is a small piece of the story. A session is a collection of events that a user triggers during a single period of activity. Think of it as a visit. If a member comes to your community forum, reads three posts, and leaves a comment, all those events (session_start, three page_views, and one post_comment) are grouped into one session.

By default, a session ends after 30 minutes of inactivity. So if that member leaves and comes back two hours later, a new session will start. This concept allows us to measure things like "events per session" or "session duration," which are useful indicators of engagement.

Users: The People Behind the Clicks

Finally, we have the user. A user represents the individual person interacting with your community site, who may have one or many sessions over time.

This seems simple, but it's one of the most common points of confusion in GA4. Why? Because GA4 has several different metrics for counting users.

As the video highlighted, here are the key distinctions:

• Total Users: Anyone who has triggered any event. This is the broadest count.
• Active Users: The number of distinct users who had an engaged session. An engaged session is one that lasts longer than 10 seconds, has a key event, or has 2 or more page views. This is GA4's primary user metric.
• New Users: Users visiting for the very first time (triggering a first_visit event).
• Users: In most standard GA4 reports, when you see a metric just called "Users," it is referring to Active Users.

For a more detailed breakdown, you can refer to the official Google documentation.

Tying It All Together

Let's visualize how these concepts fit together and map them back to our community measurement plan.

This diagram shows one user who had two sessions. In the first session, they triggered a post_comment event, which we've marked as a Key Event. In the second, they downloaded a file.

Here is how we translate the behaviors from our last lesson into the GA4 model:

Conclusion

Today, we've unpacked the core data model of Google Analytics 4. You've learned that every interaction is an event, important events are flagged as key events, events are grouped into sessions, and sessions are tied to users. You also learned the crucial difference between Total Users and Active Users, and that most GA4 reports focus on the latter.

This is a fundamental lesson that underpins everything else we'll do. You now have the vocabulary to translate your community goals into the language of analytics.

In our next lesson, we will move from the data model to the reports themselves. We'll explore the difference between dimensions and metrics—the "what" and the "how much" of your data—and see how GA4 uses them to answer questions.