WMS:Soil Type

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In the Compute GIS Attributes dialog, the soil type option determines whether a soil type coverage or a soil type grid will be used. The soil data has a slightly different meaning depending on whether CN or runoff coefficients will be computed. For CN the critical attribute is the hydrologic soil type, whereas for runoff coefficients the critical attribute is a soil ID that can be related to a table of runoff coefficients.

WMS uses integer values to store the hydrologic soil type (0-soil A, 1-soil B, 2-soil C, 3-soil D), however when reading from a database file that is associated with a shapefile WMS will read the letter values and assign the appropriate integer ID. The standard soil shapefiles distributed by the NRCS store the hydrologic soil group parameter in a separate database file than the feature polygons. This file must be joined to the attributes of the feature polygon in order to extract the hydrologic soil group parameter. In previous versions of WMS, this step had to be done outside of WMS using a GIS program like ArcView®. These tables can now be joined directly within the GIS module of WMS.


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