How to Analyze Traffic Sources in GA4: Complete Guide to Acquisition, UTMs & User Behavior

Mastering Your Audience: How to Analyze Traffic Sources in GA4 for Your Website

Understanding where your users come from is the single most critical task in digital marketing. Without accurate traffic source analysis, optimizing your marketing budget, content strategy, and website conversion paths is impossible.

Google Analytics 4 (GA4) moves beyond the static "Source / Medium" world of Universal Analytics (UA). Its event-driven model offers a far more flexible, granular, and powerful way to understand user journeys.

This guide is your practical roadmap to navigating GA4's Acquisition reports, customizing your data views, and turning raw traffic numbers into actionable growth insights for your website.

GA4's Approach to Traffic Sources: The Core Concepts

GA4's approach is built on flexibility, defined by how metrics and dimensions are measured across the customer lifecycle.

Dimension Scopes: User, Session, and Event

The first concept to master is scope. In GA4, every dimension belongs to one of three scopes, which determines the data shown in reports:

User-scoped: Attributes that stick with the user across all sessions and interactions. Example: First user default channel group.
Session-scoped: Attributes related to a single visit or session on your site. This is often the most relevant scope for initial traffic analysis. Example: Session source / medium.
Event-scoped: Attributes tied only to a specific event action. Example: Page location tied only to the page_view event.

For most traffic analysis, you will focus on Session-scoped dimensions (for comparing current marketing effectiveness) and User-scoped dimensions (for understanding initial customer discovery).

Scope	What It Describes	Example Dimensions	Best Use Case
User-scoped	Sticks with the user across all sessions and devices.	First user default channel group, First user source / medium	Understanding initial discovery and long-term value of acquisition channels.
Session-scoped	Describes a single visit from entry to timeout.	Session default channel group, Session source / medium	Evaluating current campaign performance and traffic quality.
Event-scoped	Tied to a single interaction or event.	Page location, Event name, Page referrer	Micro-analysis of behaviours on a specific page or funnel step.

Default Channel Group

The Default Channel Group is a simplified, pre-defined dimension that automatically buckets your traffic into high-level categories based on how GA4 interprets the source and medium parameters (including those from your UTM tags).

Common Default Channel Groups include:

Default Channel Group	Typical Example	Interpretation
Organic Search	source=google, medium=organic	Users who found your site via unpaid search engine results.
Paid Search	source=google, medium=cpc	Traffic from paid search ads such as Google Ads.
Referral	source=linkedin.com, medium=referral	Clicks from other websites linking to yours.
Direct	No source / medium (not set)	Users typing your URL, using bookmarks, or missing attribution data.
Organic Social	source=twitter.com, medium=social	Unpaid social media traffic from social platforms.
Email	source=mailchimp, medium=email	Traffic from email newsletters and campaigns.

UTM Parameters Revisited: The Backbone of Accuracy

GA4 cannot accurately categorize paid social, email, or specific partner campaigns without correct UTM tagging. Your UTMs feed directly into the source and medium dimensions that GA4 uses to populate the Default Channel Group.

Rule: Every non-Google marketing link should include:

utm_source (e.g., tiktok)
utm_medium (e.g., cpc or paid_social)
utm_campaign (e.g., Q4_Retargeting_Sale)

Parameter	Function	Example Values	Notes
`utm_source`	Identifies where the user came from.	facebook, tiktok, newsletter_tool	Required. Keep naming consistent and lowercase.
`utm_medium`	Describes the marketing channel or vehicle.	cpc, email, social, paid_social	Required. Must align with GA4 channel definitions.
`utm_campaign`	Names a specific promotion or initiative.	Summer_Promo_2025, Q4_Retargeting_Sale	Recommended. Use human-readable naming.
`utm_content`	Differentiates ad versions or placements.	blue_banner_v2, sidebar_link	Optional. Helps with A/B creative testing.

Navigating the Key GA4 Traffic Acquisition Reports

GA4 provides two primary acquisition reports: one for how users arrived (User Acquisition) and one for how sessions started (Traffic Acquisition).

Overview Report

GA4 acquisition overview dashboard showing user and session channel performance

Navigation: Reports > Acquisition > Overview

Purpose: Provides a high-level summary of traffic and engagement performance.

Key Cards: Look at the Users by Session default channel group card for a quick performance snapshot of your current marketing efforts, and the New users by first user default channel group for insight into how new users are discovering your site.

Traffic Acquisition Report (Session-scoped)

GA4 traffic acquisition report showing session source medium and engagement metrics

Navigation: Reports > Acquisition > Traffic Acquisition

Purpose: Analyzes the performance of the session—how did the user arrive in this specific visit? This is the most comparable report to the Source/Medium report in UA.

Primary Dimension: By default, this report uses Session default channel group.

1. Customize the Primary Dimension

This is the first action item for deep analysis:

GA4 primary dimension dropdown showing option to select session source medium

Click the dropdown menu above the table header (Session default channel group).
Change the primary dimension to Session source / medium. This provides the raw, granular data needed to debug UTM issues or compare specific platforms (e.g., google / organic vs. bing / organic).

2. Add a Secondary Dimension

To connect source data to specific initiatives:

GA4 interface showing how to add a secondary dimension like session campaign or landing page

Click the plus sign (+) next to the primary dimension header.
Add Session campaign to see performance broken down by your UTM campaigns, or add Landing page to understand which pages channels are driving traffic to.

3. Emphasize Key Metrics

Focus on these metrics to assess channel quality, not just volume:

Metric	What It Represents	How to Interpret
Sessions	Total number of visits from a source or channel.	Good for scale, but must be paired with engagement and conversions.
Engaged Sessions	Sessions with meaningful interaction such as 10+ seconds, 2+ pageviews, or conversion.	Higher values indicate traffic interest and relevance.
Engagement Rate	Percentage of sessions considered engaged.	Major quality signal. Low rate suggests expectation mismatch.
Conversions	Number of completed key actions.	Essential for channel performance evaluation.
Total Revenue	Monetary value attributed to a channel or session.	Crucial for ROAS and budget decisions.

User Acquisition Report (User-scoped)

GA4 user acquisition report showing first user channel group and new user performance metrics

Navigation: Reports > Acquisition > User Acquisition

Purpose: Analyzes the performance of the user—how did the user arrive on their very first visit? This is essential for understanding initial discovery and the ROI of top-of-funnel marketing.

Primary Dimension: By default, this report uses First user default channel group.

Value: If a user first came from a Paid Search ad, but later returns directly, the User Acquisition report still credits Paid Search. This gives a more accurate picture of acquisition impact.

Report	Scope	Primary Question Answered
User Acquisition	User-scoped	“How did this user first discover us?”
Traffic Acquisition	Session-scoped	“How did this specific session arrive on the site?”

Deep Dive: Customizing for Deeper Insights

Standard reports provide a good overview, but Explorations are where truly advanced analysis happens in GA4. They allow you to build custom tables, funnels, and segments tailored to your business needs.

Custom Reports with Explorations

Explorations allow you to build custom tables and charts from scratch, giving you full control over dimensions, metrics, and filtering logic.

Navigate: Click Explore in the GA4 left-hand navigation.

Create: Select Free-form Exploration.

GA4 exploration interface showing free-form analysis setup with dimensions and metrics

Variables Setup:

Dimensions (Rows): Import and set Session source / medium or Session default channel group.
Metrics (Values): Import and set Sessions, Conversions, and Total Revenue.
Filters: Define your segments here (e.g., filter where Session default channel group = Paid Social).

Drag and Drop:

Drag your chosen Dimensions into the Rows area.
Drag your chosen Metrics into the Values area.

Exploration Area	Recommended Configuration	Example
Dimensions	Session source / medium, Session default channel group, Landing page	Compare facebook / paid_social vs google / cpc by landing page.
Metrics	Sessions, Engaged sessions, Conversions, Total Revenue	See which campaigns drive both engagement and revenue.
Filters / Segments	Filter to Paid Social, specific campaigns, or Landing pages.	Filter where Session default channel group = “Paid Social”.

Path Exploration for User Journeys

Path Exploration visually maps how users navigate from one page or event to another. This is extremely useful for diagnosing funnel drop-offs and understanding how users behave after landing on your site.

GA4 path exploration report showing user journey flows and event sequences

Example: Start a path exploration with Session source = linkedin.com to see how LinkedIn users navigate your funnel and where they exit.

Custom Dimensions & Metrics (Advanced)

If you use non-standard tracking (like an internal campaign ID not covered by UTM parameters), you can create Custom Dimensions.

Example: If each pageview event contains an internal_tracking_id parameter, register it as a Custom Dimension and use it in Explorations alongside Session source / medium for deeper segmentation.

Interpreting Your Data: What the Numbers Mean

Knowing where to look is only half the battle. Interpreting the numbers is what drives real action.

1. Identifying Top Performers

A channel is considered a top performer if it ranks high in Conversions and Total Revenue while also showing a strong Engagement Rate.

Action: Allocate more budget to high-performing channels and examine their landing pages to replicate success across weaker channels.

2. Underperforming Channels

High traffic with low engagement or zero conversions indicates underperformance.

Action: Review ad messaging, targeting, and landing page alignment.

3. Audience Behavior Differences

Compare Average Engagement Time and Events per Session across channels to understand user intent.

4. Conversion Paths

Use the Conversion Paths report in the Advertising section to see which channels assist conversions rather than directly close them.

Insight: A channel like Paid Social might rarely be the final click, but could still be the first touchpoint for most customers.

Signal	Healthy Channel	Underperforming Channel
Sessions vs. Conversions	Both sessions and conversions increase together.	High traffic but few/no conversions.
Engagement Rate	Consistently high relative to site average.	Significantly below average.
Average Engagement Time	Users spend meaningful time exploring content.	Users bounce or leave quickly.

Best Practices for Accurate Traffic Source Analysis

Data quality determines the accuracy of your insights. Follow these best practices to ensure clean attribution:

1. Consistent UTM Tagging (The Golden Rule)

If you manage paid media, emails, or social posts, ensure consistent UTM structures for all campaign links.

Parameter	Required?	Example
utm_source	Yes	facebook.com, newsletter_tool
utm_medium	Yes	cpc, email, social
utm_campaign	Recommended	Summer_Promo_2025
utm_content	Optional	blue_banner_v2

2. Exclude Self-Referrals

A “self-referral” occurs when your own domain or payment gateway shows up as the traffic source, breaking session continuity.

Action: Add your domain (and gateways like paypal.com) to the Unwanted Referrals list in your GA4 Data Stream settings.

3. Clean Up Unwanted Referrals

Remove spammy or irrelevant referral traffic to keep your data clean.

4. Data Freshness

GA4 can take 24–48 hours to update certain metrics like conversions and cost imports. Always consider this delay when reviewing recent data.

Conclusion: Empowering Data-Driven Decisions

Mastering GA4 Acquisition reports enables you to understand exactly where users come from, how they behave, and which channels drive the most value. By leveraging scopes, UTMs, Explorations, and attribution reports, you unlock the insights needed to grow your business with confidence.