There are logical and peremptory reasons for clustering. Because of the length of nearly100 ISPs, and even more for LPs, there have been requests for “clustering” for manageability of the listings since their very beginning in 1978. In fact, in my book, Nature’s Enduring Patterns, on page 249, there is the beginning of clustering of the Principle Systems Concepts (PSCs – a phrase suggested by Richard Ericson) even before PSCs turned into Isomorphic Systems Processes and the list grew ever longer.
Here are some of the logical reasons:
- Psychological research shows humans can only handle lists of about seven variables in length before they start losing traceability. That is why there are hierarchical outlines. Note the length of your common in-country telephone number. So humans prefer long lists grouped into clusters or shorter lists of lists.