Using Digital Soil Mapping to Update, Harmonize and Disaggregate Legacy Soil Maps

Abstract

Digital soil maps are contrasted from legacy soil maps mainly in terms of the underlying spatial data model. Digital soil maps are based on the pixel data model, while legacy soil maps will typically consist of a tessellation of polygons. The advantage of the pixel model is that the information is spatially explicit. The soil map polygons are delineations of soil mapping units which consist of a defined assemblage of soil classes assumed to exist in more-or-less fixed proportions. There is great value in legacy soil mapping because a huge amount of expertise and resources went into their creation. Digital soil mapping will be the richer by using this existing knowledge-base to derive detailed and high resolution digital soil infrastructures. However the digitization of legacy soil maps is not digital soil mapping. Rather, the incorporation of legacy soil maps into a digital soil mapping workflow involves some method (usually quantitative) of data mining, to appoint spatially explicit soil information—usually a soil class or even a measurable soil attribute—upon a grid the covers the extent of the existing (legacy) mapping. In some ways, this process is akin to downscaling because there is a need to extract soil class or attribute information from aggregated soil mapping units. A better term therefore is soil map disaggregation.