What is a Source in Google Analytics?
Knowing where your website visitors come from is one of the most fundamental parts of marketing analytics. It’s the difference between blindly spending money on ads and strategically investing in the channels that actually deliver results. The metric at the heart of this entire concept in Google Analytics is "Source." This article will break down exactly what a source is, how it’s different from a medium, where you can find this in GA4, and how you can use it to make much smarter marketing decisions.
What is a Traffic Source in Google Analytics?
In the simplest terms, the source tells you where your traffic came from. Think of your website as a destination, like a store in a mall. A traffic source is the specific origin point of your visitors before they arrived at your site.
For example, if a user clicks a result on a Google search page to get to your website, the source is "google." If they click a link in a post on Facebook, the source is "facebook.com." If they click a link in your email newsletter, the source might be something you specified, like "fall-newsletter."
The source is the answer to the question: "Which specific website or platform sent this visitor to me?"
Simply identifying the website, however, is only half of the story. To get a complete picture, you need to understand the source’s partner: the medium.
Source vs. Medium: Understanding the Key Partnership
You’ll almost never see "Source" analyzed on its own in Google Analytics. It’s nearly always paired with "Medium" to create the "Source / Medium" dimension. This is one of the most important concepts to grasp in web analytics.
Source: The specific place a user came from (the where). Examples:
google,bing,facebook.com,your-partners-blog.com.Medium: The general category of how they got here (the how). Examples:
organic,cpc,social,referral,email.
Think of it like planning a trip. The source is the specific starting location (e.g., San Francisco International Airport), and the medium is the mode of transportation (e.g., airplane).
Here are some of the most common Source / Medium combinations you'll see:
google / organic: A visitor searched on Google and clicked on an unpaid (organic) search result.
google / cpc: A visitor searched on Google and clicked on one of your paid ads (CPC stands for Cost Per Click).
facebook.com / social: A visitor clicked a link from a post, profile, or ad on Facebook.
cnn.com / referral: A visitor was reading an article on CNN.com that linked to your site and clicked that link.
(direct) / (none): This one is special. It usually means the visitor typed your website address directly into their browser or used a bookmark. We'll touch on the nuances of this a bit later.
By combining Source and Medium, you get a highly specific, actionable view of your traffic. You're not just seeing that Google is a top source, you're able to distinguish between your free SEO traffic and your paid search traffic, which informs completely different strategies and budgets.
Where to Find Source/Medium Data in GA4
Now, let's find this information in your Google Analytics 4 property. GA4 has shifted some things around compared to the older Universal Analytics, but finding your traffic sources is still straightforward.
Follow these steps:
Log into your Google Analytics 4 property.
On the left-hand navigation menu, click on Reports.
In the Reports navigation, look for the Acquisition section and click on Traffic acquisition.
By default, this report shows your traffic grouped by the "Session default channel group." This is a high-level grouping created by Google (e.g., "Organic Search," "Paid Search," "Direct"). To see the more granular Source/Medium data:
Look for the table of data. Above the first column, you'll see a dropdown menu that says "Session default channel group." Click this dropdown.
In the search box or list that appears, select Session source / medium.
Voilà! The report will now update to show a table displaying all of your Source / Medium combinations, along with key metrics like Users, Sessions, Engagement rate, and Conversions. This table is your command center for understanding where your most valuable traffic is coming from.
Common Traffic Sources You'll See in Your Reports
As you explore your traffic acquisition report, you’ll start to see patterns. Here are some of the most frequent sources you'll encounter and what they mean for your business.
Organic Search (e.g., google / organic)
This is traffic from search engine users who clicked a free, non-advertised link to your site. High volumes of organic traffic usually indicate a strong search engine optimization (SEO) strategy. When you see traffic from sources like google, bing, or duckduckgo with the medium organic, you know your content is ranking and attracting visitors.
Direct Traffic (e.g., (direct) / (none))
The official definition for direct traffic is someone who typed your URL directly or used a browser bookmark. In reality, "(direct) / (none)" is Google Analytics' catch-all bucket. It's where traffic goes when GA doesn't know the true source. This can include:
Clicks from secure (https) to non-secure (http) sites.
Traffic from sources that don't pass referrer information, like some desktop email clients, mobile apps, or offline documents.
"Dark social" traffic from platforms like Slack, WhatsApp, or text messages.
A high or sudden increase in direct traffic can often point to untagged marketing campaigns, so it's always worth investigating.
Referral Traffic (e.g., forbes.com / referral)
Referral traffic comes from users clicking a link to your site from another website. This is a powerful indicator of your site's authority and reach. If you see a lot of referral traffic from industry blogs, news sites, or partners, it means people are talking about you and linking to you. These are often some of the most engaged visitors.
Social Media (e.g., linkedin.com / social)
This is traffic that comes from social media platforms. GA4 is pretty good at identifying major platforms like linkedin.com, facebook.com, instagram.com, and so on. Sometimes you might see a link shortener like t.co (from X/Twitter) show up as a referral. This is a perfect example of why controlling your own campaign links is so important.
Paid Traffic (e.g., google / cpc)
This is traffic you’ve paid for, most commonly through advertising platforms like Google Ads. The "cpc" medium stands for Cost Per Click. Properly tracking paid traffic is essential for calculating your return on ad spend (ROAS) and ensuring your marketing budget is being used effectively.
Why Does Source Data Matter? (Hint: Everything)
So why do we obsess over this data? Because a clear understanding of your traffic sources directly informs your business strategy.
Allocate Your Budget: Are you spending a fortune on Facebook Ads (
facebook.com / cpc) but finding that Google organic search (google / organic) drives more converting customers? Maybe it's time to shift some of that budget into SEO and content marketing.Focus Your Efforts: If a guest post you wrote for a partner's blog (
partners-blog.com / referral) is sending you a flood of high-quality traffic, it's a clear signal to pursue more partnerships like that one.Validate Your Strategy: Your report serves as the report card for your marketing efforts. A growing amount of organic traffic confirms your SEO work is paying off. High engagement from an email newsletter proves your content is resonating with your audience.
Troubleshoot Problems: If a previously strong source suddenly dries up, you know exactly where to start investigating. Did a partner remove your link? Did your search rankings suddenly drop for a key term?
Without this data, you're essentially driving blindfolded. With it, every decision you make is grounded in real-world performance.
Taking Control: How to Define Your Own Sources with UTM Parameters
While Google Analytics does a great job of automatically tracking sources, you should actively take control of your campaign links to ensure perfectly clean data. You do this using UTM parameters.
UTM parameters are simple tags you add to the end of a URL. When someone clicks the link, these tags tell Google Analytics exactly how to categorize that click. You've likely seen them before - they make URLs long and look complex, but their job is simple.
There are five main UTM parameters, but the three you need to know for defining your Source / Medium are:
utm_source: The source you want to see in your reports (e.g.,newsletter,instagram-profile,summer-sponsorship).utm_medium: The medium (e.g.,email,social,cpc).utm_campaign: The name of your specific campaign (e.g.,fall-sale-2023).
Let's say you're sending out an email newsletter for your big summer sale. Instead of sending a link to https://www.yourstore.com/summer-sale, you'd use this:
When someone clicks that link, they still land on the same page, but in your GA acquisition report, you'll see a clear entry like summer-newsletter / email. You'll know precisely which campaign is driving visits. This is how you turn from a passive observer to an active marketing analyst.
Final Thoughts
Understanding your traffic's source and medium is crucial for digital marketing, it's the foundation of effective strategy and decision-making. Knowing where your site’s traffic comes from and how they arrived allows you to make informed decisions about your campaigns and optimize for better results.
With all this data at your fingertips, you can take control of your marketing efforts and ensure that your strategies align with real-world performance metrics. Instead of guessing, you make decisions based on data-driven insights, leading to more effective and efficient marketing campaigns.