Cross domain tracking with Google Analytics

Yesterday when I was mentoring at Hyper Island I got a lot of questions on cross domain tracking with Google Analytics. Since I have not implemented this myself and because I dislike not knowing, I took some time reading up on the subject today.

The official documentation is good but I feel there is room for another explanation on how to implement the tracking. Here we go.

Basic Analytics tracking

Let us start with this site, vvv.tobiassjosten.net. My basic tracking code could look something like this:

var _gaq = _gaq || [];
_gaq.push(['_setAccount', 'UA-1234567-8']);
_gaq.push(['_trackPageview']);

(function() {
    var ga = document.createElement('script');
    // etc…
})();

The last bit, with the anonymous function, should always be present when implementing Analytics tracking and so I will skip it in the rest of my examples. The _gaq variable is what matters.

Subdomain tracking

Now let us say I want to add a subdomain for a site where I can post pictures of cats; cats.tobiassjosten.net. Then I would have to add the following tracking code to both vvv. and cats.. Mind the initial dot in the domain name!

var _gaq = _gaq || [];
_gaq.push(['_setAccount', 'UA-1234567-8']);
_gaq.push(['_setDomainName', '.tobiassjosten.net']);
_gaq.push(['_trackPageview']);

If I was only tracking subdomains on the same domain, that would really be all I had to do. Done!

Tracking separate top level domains

So now that my obsession with cat pictures has gotten the better of me, I want to balance it out with pictures of dogs and for that I plan to use www.awesomedogpictures.com.

I keep the tracking code on both vvv. and cats. and then add the following to my new dog site. Notice the changed domain name.

var _gaq = _gaq || [];
_gaq.push(['_setAccount', 'UA-1234567-8']);
_gaq.push(['_setDomainName', '.awesomedogpictures.com']);
_gaq.push(['_trackPageview']);

Once that is implemented I have to link the sites together. Because they are entirely different domains this requires both enabling incoming and outgoing linking.

For the incoming I add _setAllowLinker to all three sites, before the call to _trackPageview.

_gaq.push(['_setAllowLinker', true]);

For the clickable links between my sites I need to modify the anchor tags and add an onclick attribute. Here is an example from vvv.tobiassjosten.net telling the world about my new dog site.

<a href="http://www.awesomedogpictures.com/"
    onclick="_gaq.push(['_link', 'http://www.awesomedogpictures.com/']); return false;"
>Here are some awesome dogs!</a>

You do not need this linking between sites sharing the same base domain, like vvv. and cats., but only when the domains are completely different.