Projections

New Zealand Geodetic Datum 2000 (NZGD2000)

The earth is not a perfect sphere, so a system is needed to translate points into real positions on earth.  A geodetic datum defines the shape and size of the earth and the coordinate system used to map the earth. The New Zealand Geodetic datum is the official geodetic datum for New Zealand.  This was implemented in 1998 and replaced the 1949 geodetic datum.  Prior to this datum, a static datum was used.  New Zealand is located over a fault line, so with tectonic movement, the static datum would become inaccurate.  This new dynamic datum uses a deformation model to continuously update coordinates to reflect changes of the earth's surface.

World Geodetic System 1984 (WGS84)

The World Geodetic System datum is used by the Global Positioning System (GPS).  This datum is an earth fixed global reference frame.  A primary parameter defines the shape of an earth ellipsoid, angular velocity, and earth mass. 

New Zealand Transverse Mercator 2000 (NZTM2000)

The New Zealand Transverse Mercator projection is based on the NZGD2000 datum.  This projection is used when mapping New Zealand mainland.