Local mean sea level datums (LVDs)

LVDs are no longer official datums

From 1 July 2024, local vertical datums (LVDs) are no longer official datums for cadastral survey purposes and are no longer being actively maintained by Toitū Te Whenua LINZ. All vertical data will now be provided in terms of the official vertical datum, New Zealand Vertical Datum 2016 (NZVD2016), or the relevant sea surface.

There are 13 local vertical datums (LVDs) in New Zealand, and many other city or local area vertical datums and assumed height datums have been established as required. These were established by determining an approximation of mean sea level (MSL), and then transferring this level throughout a benchmark network.

Background

Sea level is not a flat or consistent surface. It varies around the coast and is affected by weather, currents, salinity and tidal forces. It is also influenced by gravity from the sun and moon, so it takes more than 18 years of observations to measure a full tidal cycle. Most occupations to determine tide gauge reference heights are significantly shorter than 18 years, so networks which have been determined using different reference points, or at different reference times, usually have different heights.

The heights on benchmarks are often based on  very long, and often poorly constrained, precise levelling networks. Others are determined over long distances by vertical angles, allowing any errors to spread and compound. Any land movement or damage to a benchmark is very difficult to determine because it  requires levelling to a stable benchmark that could be several kilometres away.

Most of the official LVDs were established and measured between 1940 and 1990, using MSL values determined prior to 1960. The heights published by Toitū Te Whenua on survey plans or in the Geodetic Database have not been routinely updated or maintained since they were observed, even though many benchmarks may have moved over time.

Geodetic Database

In contrast, New Zealand Vertical Datum 2016 (NZVD2016) heights are determined in relation to a static and stable reference surface, New Zealand Quasigeoid 2016 (NZGeoid2016). The NZVD2016 benchmark heights are regularly monitored, and because all benchmarks are included in the National Geodetic Adjustment (NGA) the relative consistency between marks can also be maintained.

• New Zealand Vertical Datum 2016 (NZVD2016)
• New Zealand Quasigeoid 2016 (NZGeoid2016)
• National Geodetic Adjustment

13 local vertical datums (LVDs)

Toitū Te Whenua provides historic height data and vertical datum relationship grids for 13 LVDs. These grids can be used to convert existing data to NZVD2016.

The distribution of these networks is shown in the image below. Note that there is overlap between some networks.

The table below provides details of the 13 LVDs, including NZVD2016 heights determined by 2 different methods to demonstrate some of the uncertainty associated with LVD measurements. 

Find out how to obtain NZVD2016 heights