Visitors are defined by a unique ID – this ID is usually stored in a visitor’s cookies
. Whenever the tracking code is executed, it looks for cookies on the browser set by the current domain. If they can’t be found, new cookies with a new ID are set. Google Analytics emphasizes visits over visitors because of the inherent inaccuracies of trying to track individual users. For example, a visitor who deletes their cookies, uses multiple browsers or shares their computer will show up inaccurately.