Google Analytics :: Tracking Code Overview

Tracking Code Overview

Google Analytics works by the inclusion of a block of JavaScript code on pages in your website. When users to your website view a page, this JavaScript code references a JavaScript file which then executes the tracking operation for Analytics. The tracking operation retrieves data about the page request through various means and sends this information to the Analytics server via a list of parameters attached to a single-pixel image request.
Because your website configuration and reporting needs might differ from a standard setup, it's a good idea to understand the general tracking process to ensure that your reports deliver data as you expect. In this way, you can decide how to configure Analytics tracking to best suit your own website.
The rest of this document covers:

How Does Google Analytics Collect Data?

The data that Google Analytics uses to provide all the information in your reports comes from these sources:

• The HTTP request of the user
• Browser/system information
• First-party cookies

The HTTP request for any web page contains details about the browser and the computer making the request, such as the hostname, the browser type, referrer, and language. In addition, the DOM of most browsers provides access to more detailed browser and system information, such as Java and Flash support and screen resolution. Analytics uses this information in constructing reports like the Map Overlay, Browser, and Referring Sites reports. Analytics also sets and reads first-party cookies on your users' browsers in order to obtain user session and any ad campaign information from the page request. The Google Analytics Tracking Code also reads the double-click cookie to get information about the Display Features.
When all this information is collected, it is sent to the Analytics servers in the form of a long list of parameters attached to a single-pixel GIF image request. The data contained in the GIF request is the data sent to the Google Analytics servers, which then gets processed and ends up in your reports. Here is an example of only a portion of a GIF request:

www.google-analytics.com/.....  

For customers that have enabled the Remarketing with Google Analytics feature, a third-party DoubleClick cookie is used to enable remarketing for products like AdWords on the Google Display Network. When this feature is used, information (including the third-party DoubleClick cookie) is similarly sent to the Analytics servers, but the example request looks like:

www.stats.g.doubleclick.net/.....

For more information on the data contained in a GIF request, see the section "GIF Request Parameters" in the Troubleshooting Guide.

How the Tracking Code Works

In general, the Google Analytics Tracking Code (GATC) retrieves web page data as follows:

1. A browser requests a web page that contains the tracking code.
   
2. A JavaScript Array named _gaq is created and tracking commands are pushed onto the array.
3. A <script> element is created and enabled for asynchronous loading (loading in the background).
4. The ga.js tracking code is fetched, with the appropriate protocol automatically detected. Once the code is fetched and loaded, the commands on the _gaq array are executed and the array is transformed into a tracking object. Subsequent tracking calls are made directly to Google Analytics.
5. Loads the script element to the DOM.
6. After the tracking code collects data, the GIF request is sent to the Analytics database for logging and post-processing.

How GIF Requests Are Classified

A GIF request is sent to the Analytics servers in the following cases and classified according to the table below. In each of these cases, the GIF request is identified by type in the utmt parameter. In addition, the type of the request also determines which data is sent to the Analytics servers. For example, transaction and item data is only sent to the Analytics servers when a purchase is made. User, page, and system information is only sent when an event is recorded or when a page loads, and the user-defined value is only sent when the _setVar method is called.

Request Type	Description	Class
Page	A web page on your server is requested.	Interaction
Event	An event is triggered through Event Tracking that you set up on your site.	Interaction
Transaction	A purchase transaction occurred on your site.	Interaction
Item	Each item in a transaction is recorded with a GIF request.	Interaction
Var	A custom user segment is set and triggered by a user.	Non-interaction

Requests classified as interaction requests will impact the bounce rate calculations for your page or site. Bounce rate is referred to as a single-page session to your site, but is strictly defined as a single interaction request during a user session. For this reason, a bounce rate for a page is also affected by ecommerce transactions and event tracking requests. This is because these features co-exist with page tracking and, when they are triggered, they result in additional interaction requests to the Analytics servers.

The GIF Request Parameters

The GIF request is quite long. Here is an example of only a part of a GIF request:

www.google-analytics.com/2/.....   

This table contains a listing of the many of the parameters passed in via the GIF Request. Not all parameters are passed in with every execution of the tracking code, since some apply only to certain conditions, such as campaign referrals or shopping carts. When using this reference, keep in mind that you will be looking for those variables that most commonly apply to the page/request you are investigating.

Variable	Description	Example Value
utmac	Account String. Appears on all requests.	utmac=UA-2202604-2
utmcc	Cookie values. This request parameter sends all the cookies requested from the page.	utmcc=__utma%3D117243.1695285.22%3B%2B __utmz%3D117945243.1202416366.21.10. utmcsr%3Db%7C utmccn%3D(referral)%7C utmcmd%3Dreferral%7C utmcct%3D%252Fissue%3B%2B
utmcn	Starts a new campaign session. Either utmcn or utmcr is present on any given request. Changes the campaign tracking data; but does not start a new session	utmcn=1
utmcr	Indicates a repeat campaign visit. This is set when any subsequent clicks occur on the same link. Either utmcn or utmcr is present on any given request.	utmcr=1
utmcs	Language encoding for the browser. Some browsers don't set this, in which case it is set to "-"	utmcs=ISO-8859-1
utmdt	Page title, which is a URL-encoded string.	utmdt=analytics%20page%20test
utme	Extensible Parameter	Value is encoded. Used for events and custom variables.
utmfl	Flash Version	utmfl=9.0%20r48&
utmhn	Host Name, which is a URL-encoded string.	utmhn=x343.gmodules.com
utmhid	A random number used to link Analytics GIF requests with AdSense.	utmhid=2059107202
utmipc	Product Code. This is the sku code for a given product.	utmipc=989898ajssi
utmipn	Product Name, which is a URL-encoded string.	utmipn=tee%20shirt
utmipr	Unit Price. Set at the item level. Value is set to numbers only in U.S. currency format.	utmipr=17100.32
utmiqt	Quantity.	utmiqt=4
utmiva	Variations on an item. For example: large, medium, small, pink, white, black, green. String is URL-encoded.	utmiva=red;
utmje	Indicates if browser is Java-enabled. 1 is true.	utmje=1
utmn	Unique ID generated for each GIF request to prevent caching of the GIF image.	utmn=1142651215
utmp	Page request of the current page.	utmp=/testDirectory/myPage.html
utmr	Referral, complete URL.	utmr=http://www.example.com/aboutUs/index.php?var=selected
utmsc	Screen color depth	utmsc=24-bit
utmsr	Screen resolution	utmsr=2400x1920&
utmt	Indicates the type of request, which is one of: event, transaction, item, or custom variable. If this value is not present in the GIF request, the request is typed as page.	utmt=event
utmtci	Billing City	utmtci=San%20Diego
utmtco	Billing Country	utmtco=United%20Kingdom
utmtid	Order ID, URL-encoded string.	utmtid=a2343898
utmtrg	Billing region, URL-encoded string.	utmtrg=New%20Brunswick
utmtsp	Shipping cost. Values as for unit and price.	utmtsp=23.95
utmtst	Affiliation. Typically used for brick and mortar applications in ecommerce.	utmtst=google%20mtv%20store
utmtto	Total. Values as for unit and price.	utmtto=334.56
utmttx	Tax. Values as for unit and price.	utmttx=29.16
utmul	Browser language.	utmul=pt-br
utmwv	Tracking code version	utmwv=1

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Ref: https://developers.google.com/analytics/resources/concepts/gaConceptsTrackingOverview
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