[defrost]

> The cartography industry and New Zealand have a long, complicated history.

Spot Quiz: What was uniquely complex about the New Zealand Map Grid (NZMG) prior to its replacement with the Zealand Transverse Mercator 2000 (NZTM2000) in 2001 ?

Bonus points to those that answer sans google, bing, AI chat, etc.

NB this is a fun question to chase down for those that like projections, casting, surveying, etc. and you'll know you've got it when you have it, so no need for spoilers. Also, not exactly strictly unique, just very uncommon globally, unique at at a national scale IIRC.

[rich_sasha]

Just a guess: it doesn't align NS-EW? Being oblong but somewhat diagonal, it makes sense perhaps to have a grid that's aligned with the major axes of the landmass. Which is not aligned with compass points.

[defrost]

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.