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If you were ever wondering what those NZTM Co-ordinates (New Zealand Transverse Mercator 2000 projection grid coordinates) on your GPS actually mean, you are likely not the only one. Many people use these every day without actually knowing much about them. For example you will often quote your location or be given a waypoint such as E1845100,N5743800.

What do these 2 sets of 7 digit numbers mean?

Firstly the two sets of numbers are grouped as:

• eastings – these are the vertical lines running from top to bottom (north to south) on a map. They divide the map from west to east. Their values increase towards the east; and
• northings – these are the horizontal lines running from left to right (west to east) on a map. They divide the map from north to south. Their values increase towards the north.

Figure 1 Example of Co-ordinates shown on a Topo50 Map, Source: LINZ Topo50 Guide

The numbers themselves are in the unit of meters. So and easting of E1845100 just means “east 1.8 million meters” or 1845.1 km from some point in the world.  e.g an easting of 1845123 is just 1 million 845 thousand and 123 meters east of somewhere (this artificial point in the world).

So where is this artificial point?

• This artificial East 0m North 0m (0,0) grid point was put in place to allow a single grid to cover all NZ legal landmass (including Ross base in Antarctica). Hence LINZ topographic maps cover all of New Zealand, offshore islands, some Pacific Islands and the Ross Sea Region with a single co-ordinate system.
• Figure 2 shows this point, as shown by the 0,0 point in the bottom left corner.

Example:

 Topo 50 Map Co-ordinate GPS NZTM Co-ordinate In reference to this 0,0 point. BF35 451 438 E 1845100 N 5743800 East 1845.1 km North 5743.8 km

NZTM Origin of Grid

Figure 2 So where is the origin of NZTM grid?