TNM seem to be flexible repository for storing knowledge. At the level of topics every understands everything. The problem is that everybody's understanding is different. So it's hard to control the consistency of the work being done. If our editors are not sure what to do, what does it all mean, and what their colleagues are doing, we'd better give up and go back to the trees.
Rooms play the role of topics and corridors are associations.
The only exception that may spoil the rule are loops, which are not present at the picure. In case of loops the travel to the leaves of the tree can be infinite, but may still make sense as the pursuit for information. But cool GUI would go further and e.g. use icon of the wall for the topics of the type city. Lots of such a modifications can be made depending on the application, but the canonical form has to be always remembered and available. I haven't seen any commercial TNM, but I'll bet, this will look like a Gordian knot.