Google Analytics generates a unique id for each visitor by using a combination of client-side and server-side techniques. Here is a simplified explanation of the process:
- When the GATC executes, it creates a first-party cookie called "_ga" in the user's browser. This cookie stores a unique identification value that serves as the Google Analytics unique id.
- The GATC also sends a request to the Google Analytics servers, including the unique id from the cookie. If the user doesn't have the "_ga" cookie yet, a unique id is generated and assigned to them.
- On subsequent visits to the website, the "_ga" cookie is sent along with the page request, allowing Google Analytics to identify returning visitors and associate their new activity with their unique id.
- Additionally, Google Analytics may utilize other techniques such as fingerprinting (collecting various browser and device attributes) to enhance the accuracy of the unique id generation, especially in cases where cookies are deleted or blocked.
It's important to note that the unique id generated by Google Analytics does not contain personally identifiable information and is primarily used for analytics and reporting purposes.