An imaginary line that connects points of equal height value eg the elevation of the land surface above or below a vertical datum, in this case of LINZ topographic mapping, this is Mean Sea Level.
Data Dictionary for contour: https://docs.topo.linz.govt.nz/data-dictionary/tdd-class-contour.html
Although captured and presented at 1:25,000 this layer, for all intents and purposes, forms part of the Topo50 map series.
Further information on Topo50: http://www.linz.govt.nz/topography/topo-maps/topo50
LINZ and our predecessors have been responsible for national topographic mapping in New Zealand for more than a hundred years.
The first digital data for the NZ Offshore Islands at 1:25,000 and 1:50,000 was created in the late 80's and early 90's by scanning the maps that existed at the time (the NZMS 272 series).
The raw data was created by photogrammetrists who from 1974 to 1997 mapped the islands from overlapping pairs of aerial photographs. Cartographers then took the data and added symbols and text, and created the colour separations needed to produce the printed maps.
The first Topo50 (2011) version of the Snares Island comprised a conversion to AKTM2000 Projection only. Edition 2.0 released in May 2014 included corrections to positional accuracy of islands and improved definition of coastline.