NZ Survey Control Networks

This dataset provides information about the survey control network, position, position accuracy, mark name, mark type, condition and unique four letter code for geodetic marks in terms of New Zealand's official geodetic datum, New Zealand Geodetic Datum 2000 (NZGD2000).

The dataset only contains marks that are within the New Zealand mainland and offshore islands. These positions have been generated using geodetic observations such as precise differential GPS or electronic distance and theodolite angle measurements. The positions are either 2D or 3D depending of the availability of this measurement data.

The source data is from Land Information New Zealand's (LINZ) Landonline system where it is used by Land Surveyors. This dataset is updated daily to reflect changes made in the Landonline.

The mark network is segmented into six control networks which provide control marks for specific purposes. The control_network field within this layer records this network with the 3 or 4 letter abbreviation code as follows:

NRF - National Reference Frame
NDMN - National Deformation Monitoring Network
RDMN - Regional Deformation Monitoring Network
LDMN - Local Deformation Monitoring Network
CHN - Cadastral Horizontal Control Network
CVN - Cadastral Vertical Control Network
BGN - Basic Geospatial Network
NHN - National Height Network

Note a geodetic mark can be in more than network. Also not all geodetic marks are currently associated with a geodetic network. Those that are may be referred to as a control mark. For more information about the control networks refer to http://www.linz.govt.nz/geodetic/geodetic-programme/survey-control-networks/.


Accuracy
============
Geodetic marks with a coordinate order of 5 or less have been positioned in terms of NZGD2000. Lower order marks (order 6 and greater) are derived from cadastral surveys, lower accuracy measurement techniques or inaccurate historical datum transformations, and may be significantly less accurate.

The accuracy of NZGD2000 coordinates is described by a series of 'orders' classifications. Positions in terms of NZGD2000 are described by three-dimensional coordinates (latitude, longitude, ellipsoidal height). The accuracy of a survey mark is indicated by its order. Orders are classifications based on the quality of the coordinate in relation to the datum and in relation to other surrounding marks. For more information see http://www.linz.govt.nz/geodetic/datums-projections-heights/heights/coordinate-orders/

Note that the accuracy applies at the time the mark was last surveyed. Refer to the web geodetic database for historical information about mark coordinates.

Note also that the existence of a mark in this dataset does not imply that there is currently a physical mark in the ground - the dataset includes destroyed or lost historical marks. The geodetic database provides more information on the mark status, valid at last time it was visited by LINZ or a maintenance contractor.