The data layer is an essential part of any analytics implementation. For online analytics, this is usually the first and most important step in analyzing data.

For example, let's say you want to track the number of visitors to your website and their characteristics. First, you need to create a data layer that will capture all the information about the visitors. You can do this by using the data layer in conjunction with a tag management system (TMS).

A TMS is a tool that allows you to track the characteristics of your website's visitors, such as their IP address, browser, etc.