NZ Cadastral Survey Network Marks

In 1876-77, J T Thomson (first NZ Surveyor General) decided on the system of plane triangulation and coordinates for all New Zealand to address surveying inaccuracies of the time and his meridional circuit system was implemented over New Zealand in 1877. This standardised the process that had previously been introduced in different provinces.

For each meridional circuit a single triangulation network provided major and minor reference stations with plane coordinates which were related to a zero value for the initial station. The coordinate system was a means to define the position of points for which two values were required. These comprised a distance, in links, north or south of the initial station together with a distance, in links, east or west of the initial station. Note 100 links is equal to 1 chain (20.12 metres). The coordinate axes extended north, south, east and west to the edge of the circuit boundaries.

The major disadvantage with the plane triangulation system was that errors were introduced due to the earth’s curvature. These errors which become more apparent when surveys crossed over into adjacent meridional circuit. To accommodate the shape of the earth the geodetic 1949 datum (NZGD49) was established which enabled the network of 'Trigs' (derived from Trigonometric station) which are still commonly identifiable by a black and white beacon situated above the mark. These trigs extended the primary network and enabled the exact bearing relationship between each different meridional circuit to be calculated. This data was captured into the 'Geodetic database in the 1980's.

Between the trigs a network of survey traverse marks have long been placed, observed and measured to as part of both geodetic surveying and cadastral surveying. These additional (low order) control marks commonly form the framework to which cadastral boundaries are connected to.

A new datum was implemented for New Zealand in 2000. The adoption of NZGD2000 (i.e. the replacement of NZGD49) has allowed closer integration with international coordinate frameworks and navigation systems. In particular, NZGD2000 coincides almost exactly with WGS84, which is the datum supporting the Global Positioning System. This enables GPS-derived coordinates to be used directly with NZGD2000 in most circumstances and was a logical choice for Landonline. The implementation of NZGD2000 required new and existing marks to be surveyed in terms of the new datum.

The historical concept of 'orders' was retained with six geodetic orders, from Zero Order (most accurate) to the Fifth Order (least accurate). Mark that were resurveyed or had their positions re-calculated (by capturing existing observed data) had a new order assigned which was a function of the standard (primarily accuracy)of the observation and the order of other control it was connected to. Other coordinates for other existing (1949) control marks were transformed and assigned a low order. The Geodetic database continues to manage many aspects relating to these marks but is linked to Landonline. Geodetic marks thus receive Landonline orders that reflect their new positional accuracies. In addition to Landonline incorporating the geodetic data, a large amount of survey control information was captured off survey plans in pre-designated survey capture areas thus enhancing the number of marks that can be used for cadastral control (6th Order). Subsequent geodetic contracts continually place and upgrade marks in the control networks along with other suitable survey marks from cadastral surveys.
In 2010 new accuracy standards were set by the Surveyor General, and some 5th order marks whose positions were originally based on data capture of old (traverse) data were downgraded to 6th order.

Most non-boundary marks that are included in new cadastral surveys that are not already geodetic control marks are intended to achieve 6th order and therefore become cadastral survey network marks.