Sand: crushed rock, shells etc smaller than 2mm in size
Data Dictionary for sand_poly: https://docs.topo.linz.govt.nz/data-dictionary/tdd-class-sand_poly.html
This layer is a component of the Topo50 map series. The Topo50 map series provides topographic mapping for New Zealand and it's offshore dependancies, at 1:50,000.
For some small islands the printed map scale is 1:25,000. Although presented at 1:25,000 this layer, for all intents and purposes, forms part of the Topo50 map series.
Further information on Topo50: