Grimm formulates the first sound shift as a system

node

The second edition of the first volume of Jacob Grimm's Deutsche Grammatik presented the Germanic consonant changes as an ordered shift affecting whole series of sounds together rather than as a list of individual correspondences. Framing the changes as a system is what converted them into a law: a systematic statement generates predictions in words not yet examined, and can therefore fail. Every subsequent development in the field — the search for conditioning factors, the doctrine of exceptionless change, the reconstruction of unattested segments — follows from treating sound change as rule-governed.

A node is not a place. Drawing it on a map would assert something about the world that no stored fact supports.