As we add each requirement to the design, we can add a link from the requirement to the design.

This gives us two very important measures:

We can easily point to the design and thus functional elements that meet a requirement

We can easily refer back from the design to the original requirement without having to trawl through a whole document. Since functional elements are very often dependent on multiple requirements from many different parts of the original document, this saves a large amount of time and confusion.

Because this inevitably makes the map very cluttered, we tend to collapse branches as we go. If you collapse a branch, and links to topics thus hidden are also hidden, allowing you to focus on small areas without getting distracted by irrelevant links: