Accuracy of the digital cadastre

Information on the digital cadastre, the Survey Conversion Project, and the Spatial Parcel Improvement project.

Origins of the digital cadastre

Introduction

The digital cadastre parcel layer is produced and maintained by Land Information New Zealand (LINZ) and is a component of the digital cadastral dataset available from the LINZ Data service and third party resellers.

The parcel layer is a digital spatial model representation of the parcel boundaries defined by approved land transfer and survey plans lodged with LINZ. The digital cadastre is used by many organisations including government departments, local authorities and private sector organisations specialising in GIS and land information systems.

Find out more aboutthe LINZ Data service

Cadastral record maps

Prior to the mid-1980s, cadastral record maps were the mechanism used to provide a seamless map of New Zealand’s land parcels. These hard copy maps were created at a variety of scales, which depended on the intensity of land use. These scales ranged from approximately 1:400 in some urban areas to 1:50,000 in remote rural areas.

As an example of the accuracy limitations of these cadastral record maps, a 1mm error on a 1:50,000 map corresponds to a 50m error in the plotted positions of the digital cadastre.

Digital Cadastral Database

From the mid-1980s, the cadastral record maps were digitised to form the Digital Cadastral Database (DCDB). Work was carried out to address some of the worst errors in the cadastral record maps, but many remained.

Some additional errors were also introduced by the digitisation process. As new survey data was submitted, improvements were made to the positional accuracy of the DCDB parcels.

Landonline

Landonline was developed by LINZ to manage New Zealand’s survey and titles systems. Between 2000 and 2002, spatial data from the DCDB was progressively added to Landonline.

Find out more about the DCDB and cadastral record maps.

The Survey Conversion Project

The positional accuracy of the DCDB data was not good enough to enable many of the benefits of Landonline to be realised. The Survey Conversion Project entered parcel dimensions (bearings and distances) into Landonline to improve the accuracy of the digital cadastre.

About 70% of parcels in New Zealand, mainly located in urban and intensive rural areas, were targeted by the project. The accuracy of about 30% of the cadastre, predominantly in rural areas, is largely unchanged from the original cadastral record maps.

Accuracy of the digital cadastre

Accuracy, particularly in non survey-accurate areas, can be variable. Every node (including parcel layer nodes) has a Landonline accuracy order which relates to the accuracy of the spatial location. Generally speaking, the spatial accuracy of a node is better where the node's position has been determined by using either surveyed bearings and distances captured from survey plans or adjusted survey data. The table below indicates the expected accuracy in survey-accurate and non survey-accurate areas.

Accuracy statusLand use95% accuracy1 Landonline accuracy order2 

Survey-accurate (bearings and distance captured from survey plans)

 

Urban

Rural

0.20

0.50

7

8

Non survey-accurate (digitisation of cadastral record maps)

Urban

Rural3

Remote rural3

5

20

100

9 or 10

10

11 or 12

1 95% of boundary points are more accurate than this value.

2 A number between 7 (most accurate) and 12 (least accurate) indicating the accuracy of boundary coordinates in Landonline.

3 In the digital cadastre a rural area is one where coordinates are mostly order 10 and a remote rural area is one where coordinates are mostly order 11 or 12.

Improving Urban Cadastral Coordinates

In 2017 LINZ began improving the accuracy of its cadastral coordinates in urban areas, to better support high-precision cadastral applications.

Cadastral co-ordinates in urban areas have been largely based on measurements initially calculated by surveyors in the early 2000s. 

Over time discrepancies of up to 10 cm have arisen in this data.

This is for a range of reasons including earthquakes, the installation of new and improved survey control marks, and slight inconsistencies between the original survey data and new data submitted by surveyors over the intervening years.  

While these discrepancies in the data are small, they are large enough to have an impact on applications such as automated testing of new survey data, precise navigation to buried survey marks, and precise visualisation of property boundaries.To resolve these discrepancies, LINZ has set up a system to combine all the cadastral measurements in an area into a single computation, generating a more accurate and consistent set of coordinates.

Benefits of this work include:

  • Reduced failures of automated business rules when new cadastral data is submitted to LINZ (this is because  the new cadastral data is now far more consistent with existing data
  • Improved consistency of digital property boundary mapping with other high precision spatial data, such as aerial imagery
  • Additional cadastral control marks are available for use by surveyors
  • Improved resilience of the cadastre to earthquakes, as land movements are easier to analyse when cadastral coordinates are accurate.

The improved data is recorded in the Landonline database and is also available via the LINZ Data Service, through updates to datasets such as NZ Primary Parcels. 

Improvements to the urban cadastral are ongoing and expected to be completed by 2020.  

For further information, please contact CRM_Geodetic@linz.govt.nz.

Last Updated: 13 March 2019