Describing soils

Soil maps and soil survey

Soils are the result of the interaction between the environmental factors geology, climate, topography, and biota over time. As these factors change across space, so do soils. And just as there are geological and topographic maps, soil maps express this spatial variability in soils.

How are soil maps made?

Soil maps are generated by a soil survey. Soil surveys require the ability to apply the data points – the soil information at individual locations, like soil pits or auger sites – to a three-dimensional landscape. As such, soil scientists need a solid understanding of how geology, climate, topography, biota, and time interact to form soil. During a soil survey, the soil scientist therefore makes intensive use of data and maps of these environmental factors. Bringing these factors and the individual data points together will eventually allow the soil scientist to identify areas in the landscape, where soil formation processes – and thus soil characteristics – are similar. These areas of similarity define the map units. By combining all the different map units, a soil map is created. Today, modern Geographic Information Systems (GIS) and geostatistical methods improve our ability to detect relationships between soils and the other environmental factors in the landscape. This contributes to better soil maps.

Reconnaissance soil map of Western Taranaki.

An example of a historic soil map. Click on the image for a high-resolution version in our Digital Library.

Scale is key

Soil maps can come in various forms and levels of detail, depending on the purpose of the mapping. First, they can differ based on the information they show in the map. Soil maps may represent the spatial variability of specific soil properties like soil depth or organic carbon content. Others show soil types from soil classification systems. Second, soil maps vary in the level of spatial detail. The level of spatial detail determines the optimal spatial scale at which the map should be used. This is particularly important to consider when ‘zooming in’. Every map has a scale limit beyond which the information of the map is no longer valid. For instance, the maps of MWLR’s S-map programme are at a scale between 1:30,000 to 1:50,000. This scale is appropriate to represent soil variability at a ~500 m length scale and more. However, they are not detailed enough to represent soils at the scale of paddocks. Achieving a higher level of detail comes at a cost though: It requires more data points with soil information, and often more detailed information on the factors that control soil formation.

A screenshot of S-map Online

A screenshot of S-map Online, the digital soil map for New Zealand. Click image to visit S-map Online

More information

Utilise S-map, our state-of-the-art digital soil spatial information system for New Zealand. S-Map data includes fundamental soil property data (e.g. depth, stoniness, clay and sand content) created from field observations and expert knowledge, as well as derived soil data based on models:
S-Map Online

Explore our historic map holdings produced Soil Survey Division and DSIR Soil Bureau between 1932 and 1989. A selection of those is available through our Legacy Map Viewer:
Legacy Map Viewer
For a full list of available map scans visit the MWLR Digital Library:
Historic maps collection in MWLR's Digital Library

New Zealand soil mapping protocols and guidelines (2017 Envirolink report):
Read full report here