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Department of Mines, Industry Regulation and Safety

The digital ‘1:500 000 State regolith geology of Western Australia’ is a compilation of existing Geological Survey of Western Australia (GSWA) regolith and surface geology maps. This product supersedes the 1:500 000 State regolith map (Marnham and Morris, 2003). While the 2003 regolith map was largely a synthesis from 1:250 000 map sources, which was partly generated by manual drawing and only used generic regolith codes, this new product incorporates all regolith coverage available at 1:100 000 scale, uses a revised regolith classification scheme, and was compiled using an automated algorithm for polygon generalization.

Regolith geology from 1:100 000 and 1:250 000 scale maps has been compiled to produce a seamless digital regolith coverage. To produce a compilation readable at 1:500 000 scale, polygon line work had to be modified. The modification included aggregation of small polygons clusters with the same code into larger shapes, elimination of microfeatures, and simplification of polygon contours, using the cellular automata (CA) model of the GeoScaler python script for ArcGIS (Huot-Vézina et al., 2012). Following this step, manual editing was required during edge fitting and topology cleaning to improve the polygon line work to comply with GSWA cartographic scale standards.

The coding of regolith units in the layer follows GSWA’s regolith classification scheme (GSWA, 2013) with the addition of a suffix representing major physiographic province subdivisions across the State. Earlier maps that did not conform to the current scheme were recoded accordingly. Regolith codes consist of three parts: primary code (landform and landform qualifier), secondary code (compositional information), and physiographic province [major physiographic subdivisions across the State based on Pain et al. (2011)]. For the scale of this product, tertiary codes (parent rock or cement) were deemed to be too detailed and were therefore rolled up into higher level codes. Regolith units are assigned to 11 landforms. They comprise areas of outcrop (_X, including bedrock and weathered rock), residual or relict material (_R, representing in situ regolith or remnants deposits from an earlier landscape), and nine transported units: _C, colluvium; _W, sheetwash; _A, alluvial/fluvial; _L, lacustrine; _E, eolian; _S, sandplain; _B, coastal (wave-dominated); _T, coastal (tide-dominated) and _M, marine. Suffixes used for the physiographic provinces are as follows: CAP, Central Australian Ranges Physiographic Province; KIP, Kimberley Physiographic Province; NAP, North Australian Plateaus Physiographic Province; NPP, Nullarbor Plain Physiographic Province; PIP, Pilbara Physiographic Province; SAP, Sandland Physiographic Province; TPP, Barkly–Tanami Plains Physiographic Province; WCP, Western Coastlands Physiographic Province and YPP, Yilgarn Plateau Physiographic Province.

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