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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 relate to one another.

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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

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.

Percent Clay

(Surface Layer), {DCP, >}, [percent]

<= 8

> 8 AND <= 16

> 16 AND <= 21

> 21 AND <= 31

> 31 AND <= 50

Not rated or not available

Santa Cruz County

Clay in Soils

10,000 0 10,000 Meters

Soil K Factor

.02

.05

.10

.15

.17

.20

.24

.28

.32

.37

.43

.49

.55

.64

Not rated or not available

Western San Mateo CountySoil K Factor

0 2.5 5 7.5 101.25Kilometers

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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.

Santa Cruz County

Soil Taxonomy Orders

11,000 0 11,000 Meters

not classified

Alfisols

Entisols

Inceptisols

Mollisols

Ultisols

Vertisols

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.