Vector GIS file set in ESRI shapefile format containing polygons of all NZ postcodes as of a particular date.

... anonymizing large address data sets, such as the one I'm working with now. One can use a postcode rather than a street or numbered address to quickly produce meaningful information about the geographic distribution of compiled demographic data, without revealing personal information. I did this a lot, using ZIP code maps, when I was a researcher in the US.

... making data available that, up to now, have been difficult or impossible to obtain.