GPS & Topo50
Some key changes in the production of the new Topo50 map series will affect your Global Positioning System (GPS) unit. Find out what you need to be aware of as a GPS user.
What has changed
On Topo50 maps, the latitude, longitude and grid coordinates (known as northings and eastings) are different from those used on the previous NZMS260 maps. This is because a new datum and projection were used to produce the maps.
The new datum, the New Zealand Geodetic Datum 2000 (NZGD2000), corresponds to the datum used in modern navigational systems, such as GPS.
The new projection is the New Zealand Transverse Mercator 2000 (NZTM2000) projection. The Transverse Mercator projection is commonly used internationally.
Relevance for GPS users
It is important that your GPS unit fits with the new datum and projection to ensure consistency with the emergency services and defence agencies. These agencies now use NZTM2000 and the Topo50 maps for their emergency and base mapping.
How to coordinate your GPS unit with Topo50
Setting the new datum, NZGD2000
For those using current GPS systems, you can change the settings on your GPS receiver to NZGD2000, the datum used by Topo50 to determine latitudes and longitudes.
If your GPS does not support NZGD2000, it will still be able to support Topo50. You can simply set your GPS receiver to the default datum setting of World Geodetic System 1984 (WGS84).
For all practical purposes, WGS84 is the same as NZGD2000. This means that latitudes and longitudes from your GPS receiver will be compatible with those shown on Topo50 maps.
Setting the new projection, NZTM2000
To get Topo50 grid coordinates (northings and eastings), check that your GPS supports the projection used for Topo50 maps, NZTM2000. Either select the appropriate menu option in your GPS unit or check the specifications in the user manual.
If your GPS does not support NZTM2000, the receiver may have the capability to input a user-defined projection. Many GPS receivers have this capability. You may need to consult the user manual on how to access this feature.
You will need to set up your receiver with the following NZTM2000 parameters:
| Projection | Transverse Mercator |
|---|---|
| Origin Latitude | 0.0 degrees South |
| Origin Longitude | 173.0 degrees East |
| False Northing | 10,000,000 m North |
| False Easting | 1,600,000 m East |
| Central Meridian scale factor | 0.9996 |
Note: this projection is the same as a Universal Transverse Mercator (UTM) but with a different origin latitude, and different false northing and easting.
More information
Find out more about GPS in New Zealand and coordinate conversions.
For more technical information on GPS units, please contact your GPS retailer or manufacturer.
