Summary

The New Zealand Map Grid (NZMG) is a projection that is used to convert latitudes and longitudes to easting and northing coordinates used for most mapping of New Zealand.

The projection is unique to New Zealand. It was designed by Dr W. I. Reilly (1973) to minimize the scale error over the land area of the country - it cannot be sensibly used elsewhere. The conversion is calculated using a complex polynomial formula. Familiarity with complex arithmetic is assumed in this description.

Note that the projection applies to latitudes and longitudes referenced to the New Zealand Geodetic Datum 1949 (NZGD49). Coordinates from other datums, such as the WGS84 datum commonly used by GPS receivers, must be converted to NZGD49 before these formulae can be applied.