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.
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 the THV web reports. THV then uses the information to see what pages are popular, the types of devices accessing the site and how you got to the site. All in all, this means we can improve the pages that are important to you and tailor them to your device.
Information adapted from Google Analytics and AllAboutCookies.org
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