<P> Other engineering soil classification systems in the United States include the AASHTO Soil Classification System, which classifies soils and aggregates relative to their suitability for pavement construction, and the Modified Burmister system, which works similarly to the USCS, but includes more coding for various soil properties . </P> <P> A full geotechnical engineering soil description will also include other properties of the soil including color, in - situ moisture content, in - situ strength, and somewhat more detail about the material properties of the soil than is provided by the USCS code . The USCS and additional engineering description is standardized in ASTM D 2487 . </P> <P> For soil resources, experience has shown that a natural system approach to classification, i.e. grouping soils by their intrinsic property (soil morphology), behaviour, or genesis, results in classes that can be interpreted for many diverse uses . Differing concepts of pedogenesis, and differences in the significance of morphological features to various land uses can affect the classification approach . Despite these differences, in a well - constructed system, classification criteria group similar concepts so that interpretations do not vary widely . This is in contrast to a technical system approach to soil classification, where soils are grouped according to their fitness for a specific use and their edaphic characteristics . </P> <P> Natural system approaches to soil classification, such as the French Soil Reference System (Référentiel pédologique français) are based on presumed soil genesis . Systems have developed, such as USDA soil taxonomy and the World Reference Base for Soil Resources, which use taxonomic criteria involving soil morphology and laboratory tests to inform and refine hierarchical classes . Another approach is numerical classification, also called ordination, where soil individuals are grouped by multivariate statistical methods such as cluster analysis . This produces natural groupings without requiring any inference about soil genesis . </P>

What are the six categories of soil types identified in the astm classification system