defining relationships between terms in a taxonomy Is there a module which allows you to define a relationship between some terms in a taxonomy? Specifically, being adjacent? The taxonomy is flat.
So that Auckland has Northland and Waikato as neighbours (the use case would be to build a view of events in nearby regions)

My searching can't have used the right names for this - I'm not finding anything :-)
The relationship functionality exists in Drupal core - no need for a contributed module.

Go to /admin/structure/taxonomy/YOUR_VOCABULARY/fields and add a new field of type Term reference, click Save.

On the next screen 


change Number of values from 1 to Unlimited
choose the same vocabulary you added the field to in the Vocabulary dropdown.


Then edit each term and add the neighbouring regions to it.