Topo50 Frequently Asked Questions

Coordinates have changed

Why were the coordinates changed?

In 2000 Land Information New Zealand (LINZ) released a new national datum, New Zealand Geodetic Datum 2000 (NZGD2000). This changed the way that coordinates (latitudes/longitudes) of points in New Zealand are determined. Latitudes and longitudes in NZGD2000 are significantly different to those determined in terms of the previous datum - NZGD1949. The difference is equivalent to an approximate 200m change in position. Subsequently LINZ has also defined a new projection for national topographic mapping, the New Zealand Transverse Mercator 2000 (NZTM2000) projection, to replace the New Zealand Map Grid (NZMG) projection. Both these changes have followed extensive analysis and public consultation.

Purchasing Topo50 maps

Where can I buy Topo50 maps?

Topo50 maps are available for sale from major map and outdoor retailers as well as Department of Conservation information centres that have retail outlets. Find a map retailer near you.

Previous NZMS260 maps

Can I keep using my NZMS260 map?

It is recommended that you switch to a Topo50 map, as these are the maps used by the emergency services. In the case of an emergency it will be advantageous to use the same maps as those used by the emergency services.

The geographical information on most maps will be the same as on a NZMS260 map. A selection of Topo50 maps will have more up to date information than the similar area on a NZMS260 map. As Topo50 maps are updated they will all eventually supercede the NZMS260 equivalent in the accuracy and currency of their geographical information.

Differences between the Topo50 & NZMS260 maps

What are the differences between a Topo50 and an NZMS260 map?

Projection: The Topo50 series uses a different projection. This means that someone reading a grid reference on the NZMS260 map will give quite a different reference to someone looking at the same geographical point on the Topo50 series. Technically this is because the Topo50 series uses the New Zealand Geodetic Datum 2000 and the New Zealand Transverse Mercator 2000 projection. This means that the point of reference for latitude and longitude and the grid coordinates of geographic features have changed. Geographic coordinates, longitude and latitude, have changed by approximately 200m, 190m in a north-south direction and 10m in an east-west direction. Grid coordinates, northings and eastings, have changed by over 550,000m in the northing and 900,000m in the easting. This difference is sufficiently large so that coordinates of the NZMS260 and Topo50 maps will not be confused.

Format: Topo50 maps are in portrait format, while the NZMS260 maps were produced in landscape. Each Topo50 map covers slightly less area, which means that there are 155 more maps covering New Zealand and that each each individual map covers a different area than on the NZMS260 maps.

Why should I buy a Topo50 map?

LINZ is the national mapping agency for New Zealand and ensures national coverage with over 451 topographic maps. LINZ has systems and processes in place to access and receive the latest information from many sources to ensure the national maps are of the highest possible quality. Maps are regularly printed to ensure they are always available and that the latest critical information is available to users and emergency services.

What is the difference between LINZ maps and other organisations' maps?

LINZ's maps are consistent in specification and cover the whole country. They are regularly updated and new editions are frequently printed. They are available from more than 400 retailers in New Zealand. LINZ maps can be used with confidence as they are used by the emergency services.

Is the information on Topo50 maps different?

The geographic features portrayed in the Topo50 map series have not changed. However the coordinates of those features have changed.

Do the new Topo50 maps cover the same area as the NZMS260 maps?

No. There were 297 NZMS260 maps covering New Zealand, while there are 451 Topo50 maps. This is due to Topo50 maps being in a new format (A1 portrait).

Why did the format change from landscape to portrait?

Changing the layout of the map distinguishes the Topo50 map series from the NZMS260 series.

Is the information on the Topo50 maps more current than the NZMS260 maps?

Generally no, however some areas will have undergone maintenance as part of the regular maintenance cycle. There will be a map available on this website which will show the currency of the data on all Topo50 maps.

Topo50 maps & GPS

My GPS is a few years old; will it support NZGD2000 and NZTM2000?

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.

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.

Find out more about GPS and Topo50.

How can I check that my GPS supports NZGD2000 and NZTM2000?

For all practical purposes NZGD2000 is the same as WGS84, the default system used by the GPS and so NZGD2000 will be compatible with your GPS.

To determine if your GPS supports the NZTM2000 projection, either select the appropriate menu option in your GPS unit or check the specifications in the user manual.

Find out more about GPS and Topo50.

Converting between NZMG & NZTM2000

How do I convert the coordinates between NZMG and NZTM2000?

The following links allow you to convert coordinates between NZMG and NZTM2000:

• NZMG to NZTM2000
• NZTM2000 to NZMG

The online conversion form allows you to make conversions between other commonly used coordinate systems in New Zealand.

What is the effect on map grid coordinates of changing from NZMG to NZTM2000?

Grid coordinates, northings and eastings, have changed by over 550,000m in the northing and 900,000m in the easting. This difference is sufficiently large so that coordinates in terms of either projection will not be confused.

Why not keep on using NZMG/NZGD1949 in my database/GIS?

The main reason for moving to NZGD2000 is to make it easier to integrate your database with other data. This may include GIS data from LINZ or other agencies that is in terms of NZGD2000, and data captured using GPS (with which NZGD2000 is closely aligned). Also NZGD2000 is much more accurate on a national scale, which is desirable for large scale datasets requiring accuracy better than a few metres.

Should I convert my geographic data to NZTM2000 or to NZGD2000?

Most modern GIS systems permit data to be converted at will between different coordinate systems. Though data may be stored in NZGD2000, it could be converted on the fly to NZTM2000, or a number of other map projections. So generally it doesn't matter which system is used.

How can I convert NZGD1949/NZMG coordinates to NZGD2000/NZTM2000?

Converting coordinates from NZMG to NZTM2000 involves three steps.

1. from the NZMG map projection to NZGD1949 latitude and longitude
2. from NZGD1949 latitude and longitude to NZGD2000 latitude and longitude
3. from NZGD2000 latitude and longitude to NZTM2000 northing and easting
   Most coordinate conversion software will perform these steps internally, so that it will appear as a direct conversion.

The first and last steps, converting to and from map projections, are mathematically exact operations. However the conversion from NZGD1949 latitude and longitude to NZGD2000 latitude and longitude is not precise - there is no exact correct way to do it. There are several options provided by LINZ with varying degrees of accuracy. For more details see converting from NZMG to NZTM2000.

What tools can LINZ provide to help this transformation?

Online coordinate conversion tool: This can be used to convert a few coordinates to a few hundred coordinates between different New Zealand coordinate systems.

To convert a large number of coordinates select advanced options, and choose free format entry for the input format, and unformatted for the output format.

Coordinate conversion software CONCORD can also be downloaded. This is a Microsoft Windows program that can be used to convert files of coordinates from one system to another.

Note: Both the online converter and CONCORD only translate individual points - they cannot convert other GIS objects composed of many points.

Why did we change the map projection?

The NZMG map projection was a unique projection crafted to minimize the scale error over the land area of New Zealand. It was specifically defined in terms of the International Ellipsoid used by the NZGD1949 datum.

NGD2000 is based on the GRS80 ellipsoid to be consistent with international reference systems. So NZMG is not an option for NZGD2000. While it would have been possible to craft a similarly optimised projection for NZGD2000 this was considered undesirable, as it would not be immediately supported by GIS and survey software vendors. Instead New Zealand Transverse Mercator 2000 (NZTM2000) was adopted, which is standard Transverse Mercator projection that software vendors can support.

Why did we change the datum?

The NZGD1949 datum was no longer accurate enough. The datum was developed over 50 years ago, and its accuracy is limited by the survey technology available at the time. The accuracy has also degraded significantly due to the natural process of earth deformation.

New Zealand Geodetic Datum 2000 (NZGD2000) was surveyed using the Global Positioning System (GPS), which provides a much higher and more uniform accuracy. It is also a three dimensional datum (NZGD1949 was a two dimensional datum), it is aligned with international datums, and takes account of ongoing deformation.