WMS:GSSHA Join SSURGO Data

SSURGO (Soil Survey Geographic database) are digital soils data produced and distributed by the Natural Resources Conservation Service (NRCS) of the National Cartography and Geospatial Center (NCGC). The database contains digital soil type and distribution information for 95% of the counties in the United States. Information covered includes soil characteristics, soil properties, and addresses limits, risks, and suitability for various uses.

SSURGO Files

The DBF file associated with SSURGO shapefiles contains the following attributes: AREASYMBOL, SPATIALVER, MUSYM, and MUKEY. Use the Join NRCS Data command to join more attributes which can then be mapped to the soil coverage.

The Join NRCS Data command opens three TXT files located in the folder containing the downloaded SSURGO data:

• "comp.txt" – Contains HYDGRP data.
• "chtextur.txt" – Contains TEXTURE data.
• "chorizon.txt" – Contains KSAT, MOISTURE, FIELDCAP, and WILTINGPT data.

Clean and Fill Values

Some SSURGO data may contain hybrid HYDGRP classes, such as "A/B." Because WMS does not support hybrid HYDGRP fields, the entry will be changed to first group listed. For example, if the entry is "B/D," WMS will change the entry to "B."

Often there are missing fields in the data. WMS provides the option to set a default value to be assigned to missing fields to avoid blanks. Set these values in the dialog shown below.

Join NRCS Data dialog

The combo boxes list the soil groups and textures that exist in the SSURGO data and are defaulted to the group and texture that occur most often.

After cleaning and filling the data, the attributes are then matched up with their corresponding MUKEY and joined to the GIS layer. If more than one entry exists for an MUKEY, the corresponding parameters that occur most frequently are joined to the layer.

It should be noted that the shapefile's DBF file is not changed in this process. If the shapefile is opened in another WMS project, select the Join NRCS Data command again in order to join the data.

Using Soil Type Data with GSSHA

GSDA soil type data can be used with GSSHA. See the GSSHA Wiki for more information. A SSURGO GSSHA soil data preparation spreadsheet is also available.