A data layer is a structured way in which a website passes information to measurement tools about what has just happened – which product the visitor viewed, what they put in the basket, what value a completed order has, or which form they submitted. Without it, measurements are set up by attaching them to the appearance of the page, for example to a button's text or to a class name in the code, which stops working at the first redesign without anyone noticing. Implementing it requires cooperation with a developer and agreement on what data, and in what structure, the website will provide. It is an investment that pays off with every subsequent adjustment to measurement and with the deployment of further tools.
See also: Tag manager, Measurement plan, Measuring e-commerce transactions.
