Explanation regarding SA1
The Statistics NZ “Small Area Unit 1” (SA1) are small areas defined by Statistics NZ. They typically have a population of 100 – 200 people and are the basic building block of all of these maps. As they represent the ‘domicile’ as collected by Statistics NZ, the SA1 have to be used to allow analysis of SNZ data including census.
In relatively sparsely populated rural areas the SA1 areas can be very large. Statistics NZ calculate a population weighted ‘centroid’ of each SA1 which is the point to which the travel time for each SA1 is calculated. This can result in some apparent anomalies, for example in the SA1 highlighted below (on the South side of the Rangitata river). The population weighted centroid is near the most populated area Peel Forest (marked as X), which is around 20 minutes drive from services at Geraldine, thus the whole SA1 is classified as R2 even though the remote Mesopotamia Station (marked as M) is included. However these anomalies are common to all the maps, and affect only a very small number of people (similar examples can be seen in other sparsely populated regions across all of the 3 maps).