Digital classification of hillslope position

Miller, B.A. and R.J. Schaetzl. 2015. Digital classification of hillslope position. Soil Science Society of America Journal 79(1):132-145. doi:10.2136/sssaj2014.07.0287.

Abstract

Hillslope position has long been important in soil geomorphology. At the scale of county-level soil maps, more soil boundaries are based on topography than any other soil-forming factor. However, the inability to accurately delineate topographic breaks across hillslopes – either due to lack of sufficient topographic resolution or the proper technology to develop/model them – hinders soil mapping efforts. In this research, we developed a decision tree model for classifying hillslope position, which was calibrated and validated using the observations of soil scientists in the field. Different decision tree structures were tested with classification breaks based on calibration groups’ mean mid-points, median mid-points, and fuzzy membership. The final model objectively and quantitatively classifies the five major hillslope positions and performs well on different landscapes, making it suitable for efficient application to large areal extents. The resulting maps of hillslope position represent base maps that can be used to (1) improve research on toposequences by providing explicit definitions of each hillslope element’s location, (2) facilitate the disaggregation of soil map unit complexes, and (3) identify map unit inclusions that occur due to subtle topographic variation. Base maps developed by the model can also help identify areas of possible inaccuracies in soil maps, especially where soil boundaries cross topographic breaks. Predictions from the model enable the mapper to better place soil map unit boundaries at locations where defendable landscape breaks exist.

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