Reading SSURGO Soils Data
Downloading SSURGO data
1. Download. You could google SSURGO download, or
just go to the Soil Data Mart:
http://soildatamart.nrcs.usda.gov/
a. Select the state (must be California for this
exercise to work), then the county, then the
survey, then Download Data…
b. You'll be submitting a request, and will need to
provide an email address.
c. It may take several minutes to an hour to get a
reply, but eventually you'll be notified via email
that a zip file is available for downloading.
2. Unzip the downloaded file, extracting into a folder
location of your choice.
3. Explore the files in the folder – there will be a folder
created there with a name like "soil_ca628" or a
different number. If you extract everything, you’ll have
one folder within the other with the same name. You
might want to rename the topmost folder something
more informative, like "MendocinoW" for the survey of
western Mendocino County, or "Amador" for the survey
of western Amador County. You will find:
 A readme.txt file with information you'll need.
 Metadata files specific to your survey. Additional
metadata about variables can be found on the NRCS
webstie, or search SSURGO Metadata. The
relevant files are currently at
http://soildatamart.nrcs.usda.gov/SSURGOMetadata
.aspx]
 Another zip file containing the database. You'll
need to unzip it.
Metadata
This guide will explore accessing particular soil
variables in SSURGO. There are many more. To
learn about particular soil attributes, explore the
metadata files on the web sites. The SSURGO
Metadata Table Column Descriptions is a good
resource. You can search it to find what file a
given attribute is located in, and it provides a bit
of description about the meaning of the variable.
Other files include diagrams of how the files
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relate to one another.
Processing SSURGO data and generating reports in Access
Microsoft Access will allow us to (1) import the highly complex SSURGO data with all data
relationships intact; (2) generate reports from the data; and (3) export these data to be readable in
ArcGIS as a map. We’ll start with the first two parts, which will provide us with a lot of
information on soils in the area we have chosen.
1. First we’d like to copy to memory (Ctrl-C or Cmd-C) the file path to the tabular data
(something like "D:\data\SantaCruz\soil_ca087\tabular\").
2.
Assuming you have access to Access, and you’ve chosen a soil survey in California
(required for this project), you should have a folder “soildb_CA_2003” or something
very similar (maybe with a different year). Make sure everything is unzipped. You
should find in this folder a file named something like “soildb_CA_2003.mdb”. Open this
file and this will start Microsoft Access.
3. If the autoexec program fails, close the window and go to the Options button in the
Security Warning bar, then click Enable Content, then Ok gets you to: SSURGO Import
4. Paste in the appropriate box the complete path to the ‘tabular’ folder in what you
extracted; this might be something similar to “D:\data\SantaCruz\soil_ca087\tabular”
5. This starts a process where it imports a bunch of text files into databases. You can see
the progress in the lower right and as names flashing by in the lower left. Then save this
database; you’ll need to point to it from the soil data viewer (below).
At this point, you should have a complete set of tables with all relationships among tables
defined. The Soil Reports form will be displayed, and this provides access to a wide variety of
reports from the data tables.
 To look at the raw tables, you can change the Navigation Pane (on the left) to show
“Tables” instead of what it currently shows, which might be “Forms” or “Reports”.
You’ll find that the tables, while intriguing, are not going to be easy to use. What you
aren’t seeing are the database relationships that tie the myriad of tables together to
provide useful information.
 Better is to either (1) generate reports, which will create the same tables that you would
find in a printed soil survey; or (2) tie these tables to a map, and explore the data linked to
the map.
 To return to the Soil Reports form, change the Navigation Pane to display Forms and
select Soil Reports. This will be your most useful place to generate reports.
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Reports
There are many different reports available. We’ll primarily be interested in:
 Brief Soil Descriptions
 Chemical Soil Properties
 Engineering Properties
 Physical Soil Properties
 Taxonomic Classification of the Soils
 Soil Features (for restrictive layers like hardpans in some soils, etc.)
Generate each of these reports for the soils in your area, and explore the results to understand
what they show. During the semester, you should learn to relate this information to what we’re
covering in the lecture.
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Creating Soil Maps
In ArcMap, we need to add the soilmu_a_ca???.shp file from the “spatial” folder of your
download. Unzip if necessary.
Soil Data Viewer must be installed, which will also install a toolbar for ArcMap. It should be
installed in 290 and the GIS Lab 272. If you are running this on a different computer on which
you can install software or extensions, download and install the free program from
http://soildataviewer.nrcs.usda.gov/ . Then proceed:
1. In ArcMap, add the soil data viewer tool bar with View/Toolbars to display the
single tool. Don’t run it yet.
2. Add the mapping unit shapefile soil map layer (soilmu_a_ca???.shp) from the spatial
folder.
3. Run the tool from its toolbar.
4. Select the soil map layer you just added.
5. If you get an error about not being synchronized, or no data match or something, most
likely the Database is set to the wrong location, as is shown below, where the map layer
is set to one from Santa Cruz County, but the database had previously been set to a
database from San Mateo County. Note that the file name – soildb_CA_2003.mdb – is
the same, but the folder name in the path identifies the location. Simply browse to
change the database to correspond to the map layer, assuming your map layer is what you
want. You’ll then see a green box at the end of the ‘Synchronization Status’ line.
The interface is somewhat similar to what we saw in the Access Reports, but we go one
level deeper here, since we will want to select a single attribute to map.
To create a map, select the attribute (try some from the Physical Properties), then click
the Map button in the Soil Data Viewer. You may have to change some settings, like
Layer options, to avoid errors related to the data you’re using. Soil surveys date from
possibly as early as the 1930’s through to the present, and methods and classification
systems have changed. The Soil Taxonomy wasn’t complete until around 1970, for
example. Thus the soil surveys don’t all work quite the same despite all of the efforts to
standardize them by the NRCS.
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Create a series of maps from the data
Soil K Factor
Western San Mateo County
Clay in Soils
Soil K Factor
Santa Cruz County
.02
.05
.10
.15
Percent Clay
(Surface Layer), {DCP, >}, [percent]
<= 8
> 8 AND <= 16
> 16 AND <= 21
> 21 AND <= 31
> 31 AND <= 50
Not rated or not available
.17
.20
.24
.28
.32
.37
.43
.49
.55
.64
Not rated or not available
10,000
0
10,000 Meters
0 1.25 2.5
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7.5
Accessing other component variables
The previous maps are fairly useful for many types of maps, and does a lot of work for you to
deal with the inherently complex nature of soil data. You should understand that soil mapping
units are inherently complex; the mapping unit polygons rarely consist of a single type of soil.
Commonly mapping units are complexes or associations of multiple soil types. A given unit
might have 55% one soil, 40% of another and 5% of other soils. However, data collected about
soils are based on the analysis of those soil series, not of the mapping unit.
The component table contains data on each of the series (or other areal type designation like
"river wash"), with a record for each component series in each mapping unit. Since this would
be a one-to-many relationship from the map unit layer, you have no choice but to set up a relate
to the component table, using mukey as the relate field. To use these data from the map, you can
do attribute selections in the component file to see which mapping units pop up. Or you can
summarize into a new map-unit related field. We’ll do the latter in Access.
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10
Kilometers
Taxonomic Classifications and Maps
One set of attributes not included in the Soil Data Viewer relate to the taxonomic class of the
soil. You can pull out the entire classification of a soil, like “FLUVENTIC HAPLOXEROLLS,
COARSE-LOAMY, MIXED, THERMIC” but if we tried to map this, we’d probably find that our map is
difficult to read since there are so many classes. It’s useful to be able to make a map of the soil orders in
our study area. While we’re at it, we’ll also pull out the longer soil mapping unit name.
Soil Taxonomy Orders
Santa Cruz County
not classified
Alfisols
Entisols
Inceptisols
Mollisols
Ultisols
Vertisols
11,000
0
11,000 Meters
What we need to do this is a table to join our spatial data to that has attributes like the taxonomic
order. We can also map the suborder, great group, etc. To do this, we’ll create a database file to
join to the map shapefile that includes all of these attributes from the ‘component’ table, using
the most common soil series in the mapping unit. We’ll start in Access.
1. With the MDB file we used earlier opened in Access, create a new query, with the Create
tab and then the Query Design selected from the ribbon. You can close the ‘Show Table’
dialog.
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2. In the View selector (on the left side of the Design ribbon), set it to SQL, and copy the
following Query text and paste it where it currently says something like “SELECT;”
SELECT component.mukey,
Max(component.comppct_r) AS MaxOfcomppct_r,
Min(mapunit.muname) AS muname,
Min(component.taxorder) AS TaxOrder,
Min(component.taxsuborder) AS Suborder,
Min(component.taxgrtgroup) AS GreatGroup,
Min(component.taxsubgrp) AS SubGroup,
Min(component.taxclname) AS TaxonomicClass
FROM mapunit INNER JOIN component ON mapunit.mukey = component.mukey
GROUP BY component.mukey
ORDER BY component.mukey DESC , Max(component.comppct_r) DESC;
3. Then press the Run button to run this query on the database. If you get any errors, is it
because you tried to type it in and made a mistake? Copy and paste usually works.
4. Go to the table view to see the result.
5. Save the query as ‘Taxonomy’ in your folder.
6. In the Navigation Pane, make sure you’re looking at Queries, and find your new
‘Taxonomy’ query, right-click it and export it to dBase IV format in your folder.
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Creating your map by joining your new table in ArcMap
If you’re familiar with ArcMap, you’ve probably created joins before. If not, perhaps this
description will work:
1. In ArcMap, add your shapefile and the dBase file
you just exported.
2. Right-click the shapefile layer in the table of
contents, then go to Joins and Relates/Join… and
use the Join Data dialog to join the dbase file to the
shapefile using MUKEY as the join field, as shown
here.
3. Now you can access the taxonomy and other fields
we added to the table. Start by opening the
attribute table by right-clicking the shapefile, and
select Open Attribute Table to see what you
have.
4. Now make a map of the great groups:
a. Right-clicking the map layer and go to its
properties
b. Symbology tab, Show … Categories …
Unique values.
c. Set the Value Field to GREATGROUP.
d. Add All Values.
e. There will be a blank row above the first type – these are non-classified soils or
sediments like riverwash or beach sands, rock outcrops, etc. Make the color gray.
f. Change colors as
desired.
g. Remove the outlines
by right-clicking any
color box, and
selecting “Properties
for all Symbols” and
setting the Outline
width to zero.
h. Ok this dialog and
finish your map.
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