Traffic dimensions help you understand how users arrive on your website or mobile app, whether that's from an advertising campaign, referral link, search engine, or another method. You can see traffic dimensions in the Acquisition reports and in Explorations.
How Analytics scopes traffic dimensions
Google Analytics groups traffic dimensions into the following scopes.
User-scoped dimensions
User-scoped dimensions are dimensions about how you first acquire users on your site or app. Because user-scoped dimensions are about how you first acquire users, the dimensions don't change when users return to your site or app. Analytics uses the words "First user" for user-scoped dimensions, as in "First user source".
Session-scoped dimensions
Session-scoped dimensions are dimensions about what lead a user to start a new session on your site or app. Session-scoped dimensions include new sessions from new and returning users. Analytics includes the word "Session" for session-scoped dimensions, as in "Session source".
Event-scoped dimensions
Event-scoped dimensions are dimensions about what lead a user to start a new session in which they perform a conversion action, such as purchase. Analytics categorizes the source and medium for non-conversion events as "(not set)". Analytics includes only the dimension name for event-scoped dimensions, as in "Source".
A user visits the Google Merchandise Store after they click a link in the description of a video on YouTube. The user views an item and then leaves the store. The same user returns the next day using a bookmark and purchases the item.
In the first session:
- First user source/medium is "youtube / referral".
- Session source/medium is "youtube / referral".
- Source/medium for triggered conversion events is "youtube / referral".
In the second session:
- First user source/medium is "youtube / referral".
- Session source/medium is "(direct) / (none)".
- Source/medium for triggered conversion events is "(direct) / (none)".
How Analytics attributes credit
By default, Analytics uses the Cross-channel last click attribution model to attribute credit for acquisitions. This attribution model ignores direct traffic and attributes 100% of the acquisition to the last channel that the user clicked. For example, a user sees your display ad and then arrives on your site for the first time from Google Search. In this example, Analytics attributes the acquisition of the new user to Google Search.
Changes to the reporting attribution model in the attribution settings are reflected in all reports with event-scoped traffic dimensions. For example, changing the reporting attribution model changes the source and medium for the add_to_cart event in all reports. User-scoped and session-scoped traffic dimensions are unaffected by changes to the reporting attribution model.
Source
Source shows where users were before they arrived on your site or app, such as a search engine or another site. For example, users who return to your site from Google Search show as "google" in the Session source dimension.
Medium
Medium shows the referring channel by which users arrive on your site or app. Channels can include:
- affiliate: users who click a link through an affiliate program
- cpc (short for cost-per-click): users who click a paid ad
- email: users who click a link in an email campaign
- organic: users who click a link from a search engine
- referral: users who click a link on a website, like a link in an article or video description
- none: direct traffic
Cost-per-click is an advertising model that bills advertisers when their ads are clicked.
Direct traffic
Analytics categorizes traffic as "direct" when no referral information is available, such as when a user arrives on your site or app directly. These include users who enter a URL in their web browser or click a link from a bookmark, mobile app, or offline document.
Source/medium
Source/medium shows both source and medium. For example, new users you acquire from Google Search show as "google / organic" in the First user source/medium dimension.
Campaign
Campaign shows the marketing campaign that referred a user to your site or app or to their newest session. You can also use the User campaign creative id dimension to see the ads creative ID associated with the ad that referred a new user.
Channel grouping
Channel groupings are rule-based definitions of your website's traffic sources that enable you to monitor the performance of all of the traffic channels coming to your website.