Understanding boundary accuracy in New Zealand

What you need to know about boundaries in GRIP

At first glance, boundary accuracy seems straightforward. However, it's crucial to understand that boundaries shown on a map are digital representations, not the actual, legal boundary locations on the ground.

Only Licensed Cadastral Surveyors have the legal authority to define the true location of a property boundary. This article helps you understand the accuracy of the boundary data displayed in GRIP—so you know what level of precision to expect for your particular use case.

Step 1: Determine the accuracy your project requires

Do you need survey-accurate boundaries?

If your work requires precise, legally-defensible boundary locations, you must engage a Licensed Cadastral Surveyor. They will physically survey and mark the boundaries on the ground.

Can you work with indicative boundaries?

If you can accept a statistical estimate of boundary locations, you can assess the likely accuracy of boundaries shown in GRIP by following the steps below.

Step 2: identify the accuracy order for the boundaries you are interested in.

The accuracy of boundaries in GRIP is determined by the "order" of the survey marks at each end of a boundary line. Each mark is assigned an order number that indicates its precision.

How to view mark order in GRIP

Turn on the relevant layer in GRIP to display survey mark information:

Steps to identify boundary accuracy in GRIP

Step 3: Identify the accuracy in metres of the boundary marks you are interested in

Once you've identified the order numbers of the marks, use the table below to understand their accuracy in metres.

Boundary accuracy by order

Accuracy status	Land use	95% accuracy (metres)	order
Survey-accurate (bearings and distance captured from survey plans)	Urban	0.20	7
	Rural	0.50	8
Non survey-accurate (digitisation of cadastral record maps)	Urban	5	9 or 10
	Rural³	20	10
	Remote rural³	100	11 or 12
Notes: 95% accuracy means that 95% of boundary points are more accurate than this value. A small percentage may be significantly less accurate (outliers). Order is a number from 7 (most accurate) to 12 (least accurate) indicating the accuracy of coordinates in Landonline. Rural vs remote rural: In the digital cadastre, rural areas have mostly order 10 coordinates, while remote rural areas have mostly order 11 or 12. Source: Land Information New Zealand

Source: Land Information New Zealand (link)

Step 4: Consider the accuracy of your context layers

When viewing boundaries overlaid on aerial imagery or other context layers, don't assume everything has the same accuracy. A mismatch between boundaries and aerial photos doesn't necessarily mean the boundaries are wrong—it could be the imagery.

4.1 Check aerial imagery accuracy

Modern regional aerial imagery typically has an accuracy of ±1 metre at a 90% confidence interval. However, accuracy can vary between datasets.

To check the accuracy of your imagery:

Click the layer information button () in the bottom-left corner of the GRIP map
Review the metadata for the aerial imagery layer
For more detail, search for the dataset name online to find full documentation

Screenshot showing example of metadata for aerial imagery in GRIP map

4.2 Account for GPS Accuracy

Consider both the accuracy of the source data, but also the accuracy of any tools you are using to navigate to the coordinate, for example it is common to be up to 10 metres out of position with a handheld GPS or a cellphone GPS - so it is worth considering this in your use of the data too.

Summary

Understanding boundary accuracy in GRIP requires considering multiple factors:

Your use case – Do you need survey-accurate boundaries or statistical estimates?
Survey mark order – Check the order numbers to determine precision
Context layer accuracy – Aerial imagery may be less accurate than boundaries
Navigation tools – GPS devices introduce their own margin of error

For any work requiring legal certainty or precise measurements, always engage a Licensed Cadastral Surveyor.