SEO & Content Marketing Hub

I’ve personally used Google Analytics – in all its versions – for over 15 years. While even a contributor to GA4 (Krista Seidan) says “sorry” for creating it (in jest), we have to live with it.

If you’re anything like me you’ve spent hundreds of ours building reports like second nature in Google Analytics, but sometimes you just can’t actually, really, define what some of the vocabulary means.

I’ve forever gone straight to “source / medium” and paired with the landing page report to get what I needed and zip in and out like second nature. GA4 has greatly expanded the feature set, but I love that we still have the classics breakdowns.

Ok so first, let’s define each of these:

1. What is “source” in GA4?
2. What is “medium”?
3. What is “channel”?
4. How do they relate to each other
5. Give me examples

The Triumvirate of GA4 Acquisition Data

The core of understanding how people find your website lies in three key dimensions: Source, Medium, and Channel. While they seem similar, they provide different levels of granularity for attributing a user’s visit. Grasping the distinction is the first step to building accurate GA4 reports and making informed marketing decisions.

What is “Source” in GA4?

The Source is the specific origin of your traffic—the actual entity or platform that sent the user to your site. Think of it as the “where” the user was right before clicking your link. It’s the most granular level of identification.

When Google Analytics records a session, it looks at the referrer (the previous page’s URL) to automatically determine the source. If you’re using UTM parameters, the utm_source tag overrides the automatic detection.

Source Examples:

1. google: Traffic from the Google search engine, Google Ads, etc.
2. facebook: Traffic from Facebook.
3. (direct): The user typed your URL directly into the browser or used a bookmark (no referrer data).
4. linkedin.com: Traffic from a specific link on a LinkedIn article or post.
5. newsletter_q2_2025: A specific custom name you used for an email blast’s utm_source.

What is “Medium” in GA4?

The Medium is the general category or method of acquisition. Think of it as the “how”—the type of marketing or delivery mechanism used to bring the user to your site. It is less specific than the source and is a high-level grouping of traffic types.

GA4 often auto-populates this dimension based on the source (e.g., if the source is any known search engine, the medium will be organic). When using UTM tagging, the utm_medium parameter is what defines this value.

Medium Examples:

1. organic: Non-paid traffic from search engines (Source: google, bing, etc.).
2. cpc: Cost Per Click (paid search ads, often Source: google).
3. referral: Traffic from a link on another website that isn’t a search engine or social site (Source: custom-blog.com).
4. email: Traffic from any email marketing campaign (Source: mailchimp, newsletter).
5. (none): The medium for Direct traffic (paired with Source: (direct)).

What is “Channel” in GA4?

The Channel is the broadest, most general grouping of traffic. It is a powerful, rule-based categorization system that combines various Sources and Mediums into a handful of standardized, high-level groups. GA4 uses its “Default Channel Grouping” to do this automatically, ensuring your traffic is categorized consistently across all reports, regardless of your granular UTM tagging.

For example, GA4 knows that the combination of Source: google and Medium: organic belongs to the Organic Search Channel, while Source: facebook and Medium: cpc belongs to Paid Social. This standardization is key for comparing performance across marketing silos.

Channel Examples (Default Channel Grouping):

1. Organic Search: Groups all non-paid search traffic.
2. Direct: All (direct) / (none) traffic.
3. Paid Search: All pay-per-click search engine advertising.
4. Organic Social: All non-paid traffic from social networks.
5. Email: All traffic categorized as coming from email campaigns.

The Relationship: From Specific to General

You can think of the relationship between these three terms as a hierarchy moving from the most specific detail (Source) to the broadest category (Channel):

• Source: The specific machine. (e.g., google)
• Medium: The type of energy/mechanism. (e.g., organic)
• Channel: The overall power grid/category. (e.g., Organic Search)

In short, the Source and Medium determine the Channel via pre-defined rules. The Source / Medium is a combined dimension that provides the ultimate clarity on where and how a user arrived, and it remains the gold standard for granular analysis in GA4.

Now that we have these definitions, let’s look at the data you’ll typically see…

Seeing the Data: How Source / Medium Forms a Channel

The **Source / Medium** pairing is critical because it’s the exact data point GA4 uses to execute the “Default Channel Grouping” rules. Understanding these common pairings will immediately clarify your reports and help you troubleshoot any miscategorized traffic that shows up in the dreaded **Unassigned** channel.

Common Source / Medium Combinations and their Channel:

Below are five common scenarios that illustrate how the granular Source and Medium values are rolled up into a Channel:

1. Scenario 1 (Organic Search):
   • Source: google
   • Medium: organic
   • **Channel:** **Organic Search**
   • **Why?** GA4 recognizes the medium as “organic” and the source as a known search engine.
2. Scenario 2 (Paid Search):
   • Source: google (or bing)
   • Medium: cpc (or ppc)
   • **Channel:** **Paid Search**
   • **Why?** The medium matches one of the defined paid search terms (Cost Per Click/Pay Per Click).
3. Scenario 3 (Direct Traffic):
   • Source: (direct)
   • Medium: (none)
   • **Channel:** **Direct**
   • **Why?** This specific pairing signals a lack of referrer data, meaning the user arrived directly.
4. Scenario 4 (Organic Social):
   • Source: facebook
   • Medium: social (or social-media)
   • **Channel:** **Organic Social**
   • **Why?** The medium matches a predefined social term *or* the source matches a known list of social domains.
5. Scenario 5 (Referral):
   • Source: techcrunch.com
   • Medium: referral
   • **Channel:** **Referral**
   • **Why?** The traffic came from a third-party website, but the medium is neither a classified paid nor social type.

The Importance of UTM Parameters in GA4

While GA4 does a great job of automatically classifying the majority of your traffic (especially Google Ads and organic search), the moment you run a campaign outside of Google’s auto-tagging ecosystem—like email, social posts, or banner ads on a partner site—you must use UTM parameters.

UTM tags are small snippets of code you add to the end of a URL to manually define the source, medium, and campaign name. They are your quality control mechanism for acquisition data. If you don’t tag a link, you run the risk of having valuable campaign traffic fall into the generic **Referral** or, worse, **Unassigned** channels, making it impossible to evaluate performance accurately.

For example, instead of sending a link as:

https://www.yoursite.com/sale

You would tag a paid Facebook ad as:

https://www.yoursite.com/sale?utm_source=facebook&utm_medium=cpc&utm_campaign=winter_sale_2026

This simple act ensures GA4 records the visit correctly as:

• Source: facebook
• Medium: cpc
• Channel: **Paid Social**

Without those UTM tags, that same traffic might just show up as facebook.com / referral, giving the impression it was an unpaid post, completely skewing your ROI calculations. **Accurate attribution begins and ends with correct UTM tagging.**

Let’s Show a Bunch of the Top Acquisition Paths

There’s nothing better than examples. Using Gemini to help compile, I pulled after a request, the top sources, mediums, and channel paths as well as common compbos. I personally find this extremely helpful. I read the top ranking blog posts in Google search on the subject and none of them where as good as this!

This is a comprehensive list of the most common values for each of these dimensions, based on standard GA4 reporting and general web traffic patterns. These are the values you are most likely to see, which typically represent the highest traffic volumes.

Table 1: Top GA4 Sources (Estimated Popularity)

This is Gemini’s best ranking of popularity as of October 23, 2025. I trust this because Gemini does a pretty solid job of inferring rankings. I would cross-check this with official reports from inside your company as well as 3rd party data.

Note: (direct) is technically a Source value for direct traffic, often paired with the Medium (none) or (not set). For many sites, referral sources (like custom-site-1.com) and paid sources (like adroll) will appear further up the list.

Table 2: Top GA4 Mediums (Estimated Popularity)

Table 3: Top GA4 Default Channel Groups (Estimated Popularity)

Table 4: Top 50 GA4 Source / Medium Combinations (Estimated Popularity)