Data Provenance

Changes in the August 2019 data update

The following is information on some important changes we have made to S-map in this release.

  • New areas of S-Map in this update include Lyttleton Harbour, upper Waimakariri (Canterbury), Inangahua (West Coast), Wairarapa, and Rarangi (Marlborough).
  • For the Hawkes Bay there is a regional map update, with new mapping to infill gaps of the high country, and elsewhere some adjustments to map units has improved merging of soil surveys and the continuity of the soil mapping throughout the region.
  • Updates have also occurred to some areas of other areas, through an internal S-Map database quality assurance system that identifies siblings with mutually inconsistent soil properties. For example, a sibling classified as Gley soil order cannot be well drained. Siblings that were entered more than 8 years ago were not subject to these comprehensive QA checks. This update includes corrections to many of the early siblings, including soil classification, root barrier, depth and estimates of clay, silt, sand content. The corrections are usually minor but in a few areas are likely to result in small changes to estimates of the soil moisture content values used in OVERSEER and profile available water.
  • Minor issues with the geometry from the first areas to go into the S-Map database have been corrected including very small gaps, slivers, tiny polygons and some larger overlapping polygons.


More on data provenance

Inherent in the design of S-map is provision of estimates of thickness of soil layers and of their physical characteristics, together with estimates of the proportion of siblings (soil types) that occupy map units. Provision of this quantitative data is challenging because soils are highly variable in both the horizontal and vertical dimensions. Accuracy of information within a map unit is therefore dependent on the amount of site data available for any map unit.  While all reasonable skill and care have been exercised in the collection and preparation of this data, the Data Providers can give no warranty that the data supplied are free from errors, omissions or other inaccuracies. 

Confidence measures

A general indication of accuracy may be found in the confidence rating assigned to map unit composition.  Each sibling with a map unit is assigned a confidence rating of High (H), Medium (M) or Low (L).

  • The H and M ratings relate to confidence in the proportional value of the soil sibling (or functionally similar siblings) occurring within the map unit. 
  • For a High confidence map unit with a single sibling, the sibling should be found in at least 80% of the map unit (i.e. 100±20), as opposed to at least 60% (i.e. 100±40) in a Medium confidence map unit.
  • For a double symbol map unit it is likely that areas for both siblings will be within ±10 in a High confidence map unit, and ±20 in a Medium confidence map unit.
  • A rating of L (Low) is used where the pedologist has less confidence in the identified sibling or its proportion due to lack of data or insufficient resources to verify the data.  This will usually occur where the sibling(s) have been assigned based on a soil-landscape relationship and aerial photo interpretation, rather than a site visit with direct observation (auger holes or soil profile descriptions).  

Map units have been mapped on a topographical base (Topo50 series, NZ 260 series or NZMS 1) and are designed to be used at scales between 1:50000 and 1:20000.

Users should consider both the scale at which they are applying the data and the map unit confidence code, and take responsibility for the impact these may have on any decisions arising from their data use. 

Manaaki Whenua shall not be liable on any legal basis (including without limitation negligence) and expressly excludes all liability for loss or damage howsoever and whenever caused to a user of the maps, factsheets or other information provided by this web site.


Last updated: 27 August 2019