Map of NZ's Extended Continental Shelf, J. Black / GNS
The art work is located at the geographic centre of New Zealand's Extended Continental Shelf. It was designed by Billy Apple and installed by DoC and GNS Science in March 2019.
New Zealand lodged its submission under the UN Convention of the Law of the Sea (UNCLOS) in 2006. The submission establishes the precise outer limits of the ocean floor, or "continental shelf" under our jurisdiction. The boundary of the continental shelf is depicted on the art work.
The geographic centre can be thought of as the "balance point". If you were to cut out a model of NZ's continental shelf, the centre is the point it would balance at. It is a pure co-incidence that this location happens to be on land, and very special that it is in a moderately accessible location (for hikers!) with great views.
The nearby outcrops of rock along the track, reveal the underlying bedrock that makes up the Tararua ranges. It is sedimentary sandstone and mudstone (greywacke) laid down in the deep ocean off the coast of Gondwanaland, a long time before modern New Zealand was uplifted along the present day plate boundary. The Tararuas have been pushed up above the Wairarapa plains along major active faults over the last 1.5 to 2 million years. Where you are standing is located between the Wellington Fault (running up the Tauherenikau Valley to the west) and the Wairarapa Fault (at the base of the Tararuas to the east).