GSDA:Obtaining Soil Type Data from NRCS - SSURGO
The NRCS offers two different types of soil type data, namely statsgo and ssurgo. The statsgo data is at a state-wide level, while the ssurgo data is county-wide. The ssurgo data has a finer resolution. The NRCS offers the ssurgo data in a variety of file formats, including DLG(3), Arc/Info Coverage, Arc/Info exchange file (*.e00), and Shapefile (*.shp). For WMS users, the format of choice would be Shapefile, since it can be imported directly into WMS. However, a user owning an Arc/Info or Arcview license can download the Arc/Info Coverage and use Arc/Info or Arcview to convert it to a shapefile.
At the time of composing this page, the NRCS is still converting the county data to the Shapefile format, but is projected to be done in two years or less. As the shapefile data is created, it is posted on the SSURGO website. To date, over 500 counties have the option to download the soil data as a shapefile.
To download soil type data from the NRCS SSURGO website:
- Go to the SSURGO data web page, found at www.ftw.nrcs.usda.gov/ssur_data.html
- Click on the Download SSURGO Data link, located towards the bottom of the page.
- Create a new account if you haven't already done so.
- Enter your username and password.
- Click the Download button next to the county of choice.
- Click the shp.zip button to download the shapefile.
If the NRCS has not yet compiled a shapefile for your county, you will not see this button.
- Choose to Save the file to your computer.
- Unzip the shp.zip file.
- Unzip the attribute data zip file.
Note: The file named comp.txt contains the Hydrologic Soil Group field, which you will need to join to the soil type polygon shapefile.
To join the Hydrologic Soil Groups to their respective soil type polygons, you can either use the Excel Template provided below, or use a GIS Application, like Arcview.
Help – performing a Join with Arcview
The shp.zip file contains a folder name "shp." Within this folder you will find several shapefiles; the shapefile containing an "_a" contains the soil type polygon shapes. For example, one might see the following files within the shp directory:
The file named sc069_a.shp contains the soil type polygons and is the file you would want to import into WMS.
Notice that the shp folder contains an additional zip file. This second zip file will have an extension of *.gz and its name will be comprised of the two-letter state abbreviation plus 3-digits (for example, "sc069.gz"). This zip file contains a series of text files (*.txt). These files contains attribute data for the soil type polygon shapefile. Continue with the following steps:
The ssurgoImport.xls Template:
This spreadsheet template contains macros that are designed to:
- Quickly import the comp.txt file, which contains the soil attribute data for the polygon shapefile
- Join its Hydrologic Soil Group field to the shapefile attribute table
- Save out the new shapefile attribute table containing the Hydrologic Soil Group (A,B,C, or D) for each polygon record
This template was especially designed for WMS (Watershed Modeling System) users who are obtaining soil type shapefile data from the NRCS SSURGO website.
The NRCS also provides a Microsoft Access template for reading the text file data located in the attribute data zip file. This template is more robust for more general GIS applications and enables users to quickly produce reports from the attribute data. This template, along with information on its use, can be obtained from the NASIS (National Soil Information System) web site at http://nasis.nrcs.usda.gov/downloads/.
- This template contains macro programs. In order to function, you will need to make sure that Excel's security level is set to medium before opening the template. This can be done by selecting Macro from the Tools menu, then selecting Security...
- This template is designed to work in Excel 2003. To be able to use it in Excel 2007, you will need install an excel add-on that allows you to save *.dbf files