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Tracking Domains & Subdomains with Google Analytics

In this lesson, you will learn:

  • when to track across domains using the _link() method
  • when to track across domains using the _linkByPost() method
  • how to track across subdomains
  • best practices for tracking across subdomains
  • how to track across multiple domains with subdomains

Tracking Across Multiple Domains

So far in this course, we’ve focused on tracking within a single domain. Before we learn how to track across multiple domains, let’s understand why we might want to do this. A domain is a hostname that represents a numeric IP address on the internet. It allows us to easily identify a website by a name instead of having to use a long string of numbers. For example, Google.com and YouTube.com are both domains owned by Google.

You may sometimes need to track activity across multiple domains. A common example of this is when you send visitors from your site to a separate shopping cart site to complete their purchases. However, since Google Analytics uses exclusively first party cookies, it can’t automatically track whether those visitors actually complete a purchase or not, because the purchase is taking place on another site. Phrased more generally, if a session spans multiple domains, it would not be possible to track the session as a single visit attributed to one visitor. So, you’ll need a way of sharing the cookie information between the two domains.

By calling the _link() method, you can send this cookie information across domains. This allows Google Analytics to track a user across multiple domains by sending cookies via URL parameters.

To track across domains, you’ll need to follow two steps. First, add a few lines to the Google Analytics Tracking Code on all pages of each site. The lines you need to add are shown here, in blue. Call _setDomainName() with an argument of “none”. And call _setAllowLinker() with an argument of “true”.

The second step involves the _link() method. Use this method in all links between domains. In this example, we’re updating all links from Google.com to YouTube.com and vice versa. We update each link to call the _link() method as shown here. Now, when a user clicks on a link that takes them to the other domain, the session information is preserved and the user is identified as being the same visitor across both domains.

If you use a form to transfer your visitors from one domain to another, you will need to use the _linkByPost() method instead of the _link() method. This situation occurs most often with third party shopping carts. To use forms to transfer from one domain to another, you must modify all the appropriate forms with the code shown here. The _linkByPost() method will change the form action by adding query-string parameters to the value in the action attribute when the visitor submits the form.

Tracking Across Multiple Subdomains

You may also sometimes need to track across multiple subdomains. A subdomain is part of a larger domain and frequently each subdomain contains the pages for a specific department or offering. For example, Google.com has several subdomains such as news.google.com, sites.google.com, and maps.google.com. Since Google Analytics uses first-party cookies, cookies set on a subdomain can not automatically be read on the main domain, and vice versa. As with multiple domains, you need to explicitly share the cookie information between subdomains or you’ll lose session information. If you don’t share cookie information between your subdomains, it may appear as though your own site is a referrer since only one domain is recognized as the main domain.

To track across multiple subdomains, call _setDomainName() and specify your parent domain name as the argument. This will allow the Google Analytics Tracking Code to use the same cookies across the subdomains. For example, to track across Google’s various subdomains, you would call _setDomainName() with an argument of “dot google dot com”. A side effect of using this method is that your reports may not differentiate between visits to identically named pages within the various subdomains. So, for example, visits to maps.google.com/home.html and mail.google.com/home.html would be interpreted as visits to a single page. To correct this, you’ll need to set up an advanced filter. We’ll explain this in a minute.

There are a few best practices for setting up your Analytics account to track across multiple subdomains. First, create separate profiles for each subdomain. This way, you’ll be able to see reports for each subdomain. Set up duplicate profiles - one master profile, plus one profile for each subdomain. In this example, we’re looking at two subdomains. Your master profile has no filters, and each of the other two has an Include filter. Profile 1 includes all traffic to both subdomains. Profile 2 includes only traffic to subdomain A. Profile 3 includes only traffic to subdomain B.

Second, if you track across several subdomains within one profile, your reports may not differentiate between visits to identically named pages within the various subdomains. This is because the reports only show the Request URI -- which, in this example, is /home.html. The hostname -- maps.google.com -- is stored in the Hostname data field in Google Analytics. So, once you’ve called _setDomainName() to set your primary domain name, visits to maps.google.com/home.html and mail.google.com/home.html would be interpreted as the same page--”/home.html”. To correct this, you can set up an advanced filter to include the subdomain in your reports. Set up your filter as shown in the slide. Note that the constructor must match exactly what is shown in the slide, starting with the forward slash. The filter works by appending the Hostname to the Request URI. As a result, you’ll be able to distinguish between identically named pages on your subdomains.

Tracking Across Multiple Domains with Multiple Subdomains

If you want to track across both multiple domains and subdomains, you’ll need to ensure that the Analytics cookies are set across the subdomains and that the cookies are being passed between the parent domains. There are two steps. For the first step, add the lines of code shown in blue to Google Analytics Tracking Code on every page of of one of Domain 1 and each of its subdomains. Make sure that _setAllowLinker() has an argument of true and _setAllowHash() has an argument of false. Then, to each page of Domain 2 and each of its subdomains, add the same code -- but with a different argument to _setDomainName().

For step 2, call _link() or _linkByPost() in all links and forms that cross between the two parent domains. For example, the code shown in the slide shows how you’d do this to track across Google.com and YouTube.com. Note that you don’t need to use _link() or _linkByPost() in links between subdomains within the same domain. Again, you should create separate profiles in your account for each primary domain and/or each subdomain. You can easily do this by using an Include filter based on the hostname field.

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