the south island is the least populated island so my guess is it is some where in there.
new Plymouth
Australasia is the regional name for NZ and Australia. [austral = southern]
Australasia is a regional name that includes both New Zealand and Australia, and Oceania is an even broader regional name encompassing much of the Pacific. Polynesia is a rather more specific...
I guess you mean the THERMAL regions, in which case, the Taupo Volcanic Zone is the general answer, and possibly the Rotorua region in particular.
Alaska with population density of 1.2 person per sq. mi.