When we talk about Web Analytics we often talk about cookies like they’re the be all end all. The last step. But cookies don’t calculate, they don’t execute, and they certainly don’t report. Cookies in GA function a little like RAM: they hold data for computation, gathered by javascript and appended to a request to Google Analytics servers for __utm.gif. (I’m leaving the two underscores out from now on)
So you can look at your cookies all you want, but what’s going to show in your analytics is that which is sent along with the request for utm.gif. (though they should be the same, right? The UTM.gif uses a series of query parameters (which we mentioned in the last RUGA post) appended to the image call in order to communicate your data to Google Analytics servers, making it kind of the be all end all for what data is making its way into your analytics reports. As well as more specific data, each request can contain a series of more general queries, including:
utmac
utmac notes your account. (eg UA-1234567-8) I shouldn’t have to explain why GA needs this.
utmcc
This string denotes the cookie values requested from that page. It includes the data from your utma and utmz cookies cookies, or what not.
utmn
The most obvious potential problem with this has to do with caching. Most browsers will cache an image so that future requests don’t need to keep asking for it from the server. If a .gif request isn’t being made of the GA server, then data isn’t being gathered. The utmn variable exists to prevent caching. utmn is a random number generated for each utm.gif hit, assuring that each request is original and thus the image does not get cached.
utmwv
urmwv literally just tracks the version of ga.js that sent the request. Nothing special.
utmt
There are multiple types of requests that GA can execute. utmt records the type of utm.gif hit, including custom variables, events, ecommerce items or transactions. In some cases this variable wont be sent, in which case the request is defaulted to “page”.
Next week we’re going to get into the meat of this by looking at pageviews and how cookies and the utm.gif track details of your page.
