Good guess; the alignment of the spine of the two islands was the motivation for the type of projection used .. that leaves the what type, why complex, and why

Good guess; the alignment of the spine of the two islands was the motivation for the type of projection used .. that leaves the what type, why complex, and why rare / unique bits. Many years back I had the task of writing code for this (and many other types of projections) from first principles to compare against the "official" implementation released by the NZ cartographers .. it's a fun one.