It turns out there's an exact middle of Middle Earth.

Scientists have joined renowned conceptual artist Billy Apple in marking the centre of New Zealand's extended continental shelf.

This vast area – on which our islands sit - measures six million square kilometres and is 14 times the size of California, or about one per cent of the surface area of the Earth.

As 95 per cent of the territory is underwater, the area is about 22 times the area of New Zealand's landmass.

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While the centre of the country had long been marked by a monument in Nelson, the true point, geographically, happened to about 6km down a track in the Tararua Ranges, about 11km northwest of the Wairarapa town of Greytown.

More than a decade after the UN recognised New Zealand's territory included our undersea continental shelf as well as the land mass above the sea – adding an extra 1.6 million sq km of seafloor to our exclusive economic zone – this spot has been marked with a new plaque.

The circular stainless steel artwork, which is 1m in diameter, was installed with the aid of a helicopter.

The image on the plaque shows the outline of the main islands that make up New Zealand sitting inside the silhouette of the extended continental shelf boundary.

The exact coordinates of the geographic centre are inscribed around the plaque: 175° 21.737'E, 41° 1.093'S.

Its designer, Apple, who is best known for his work in the pop art movement of the 1960s and conceptual art in the 1970s, had wondered about the centre of New Zealand for decades.

During the 1970s this was a conceptual art question he posed to reveal the nature of exhibition spaces.

He approached GNS Science about creating an artwork based on a large survey pin that would mark the geographic centre of this vast land and marine territory.

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GNS Science researcher Jenny Black carried out the calculations that identified the centre as being on Department of Conservation land in the Tararua Ranges.

DoC helped to install the stainless steel artwork beside the Mount Reeves Track, which ran close by the centrepoint.

Cornel de Ronde and Jenny Black of GNS Science with the new plaque that marks the centre of New Zealand's Extended Continental Shelf. Photo / Supplied
Cornel de Ronde and Jenny Black of GNS Science with the new plaque that marks the centre of New Zealand's Extended Continental Shelf. Photo / Supplied

Apple said his focus on art and life meant that his work dealt with real issues.

"The collaboration with Cornel de Ronde and his team at GNS Science has been a great opportunity and keeps art relevant."

DoC's Wairarapa operations manager Kathy Houkamau said Wairarapa and the Tararua Ranges had always been considered to be the heart of the country.

"It's nice to discover this has geographic truth - we hope this encourages more people to get out and explore Wairarapa's natural spaces," she said.

De Ronde said the plaque signified a new way of understanding our place in the world.

"It's a small but important reminder that our continental land mass does not end at the coast line, but extends out beyond the horizon," he said.

New Zealand's extended continental shelf measures around six million sq km. Image / GNS Science
New Zealand's extended continental shelf measures around six million sq km. Image / GNS Science

"The underwater territory straddles the boundary between the Pacific and Australian Plates and includes submarine volcanoes and a subduction zone that is part of the Pacific Ring of Fire.

"Because of this, it is potentially the source of large earthquakes and tsunamis.

"We need to explore this underwater frontier so we can better understand the underlying geology of our country and enhance our ability to deal with the natural hazards."

HOW TO GET THERE

Park in the carpark at the end of Waiohine Valley Rd, about 10km from Greytown in Wairarapa. Follow the Mt Reeves track on foot for about 6km. The track is well marked with orange DOC triangles. A reasonable level of fitness and good footwear are recommended.