NO. 49 DATE 04/18/01

Range

Soils/geology

The Soils Suitability

Extension (SSE)

by Mary Beth Stulz, 

GIS Development Specialist, National

Science and Technology Center

Background

The National Science & Technology

Center (NSTC) has developed the

Soil Suitability Extension or SSE,

which is a customized ArcView GIS

extension. Extensions are add-on programs that provide specialized GIS

functionality. SSE allows someone

with minimal ArcView skills and

without a soils background, easy

access to existing soils data. SSE provides the user with quick and easy

access to the Natural Resources Conservation Service (NRCS) State Soil

Geographic Database (STATSGO)

and Soil Survey Geographic Database

(SSURGO) data with a number of

predefined queries.

The NRCS is responsible for collecting,

storing, maintaining, and distributing

soil survey information. Millions of acres

of soil surveys have been completed, and

many of these are on Public Lands. In

preparing a soil survey, soil scientists,

conservationists, engineers, and others

collect extensive field data about the

nature and behavior characteristics of

soil. Data is collected on soil properties,

erosion, drought, flooding, and other factors that affect various soil uses and management. Soils data is stored in tables that

relate to the individual mapping unit.

Types of Soil Surveys

NRCS has established three geographic

databases representing soil maps and

related variables compiled at different

scales. Table 1, NRCS Soil Geographic

Databases, summarizes the primary uses,

scales, and sources for each of the three

databases. Each map unit is linked to

attribute data files containing soil properties and interpretive information. The

NRCS Soil Interpretations Record database contains the attribute information

for each database.

STATSGO was compiled for each state

and designed primarily for regional,

multi-state, river basin, state and multicounty resource planning, management,

and monitoring. STATSGO data is not

sufficiently detailed to make interpretations at the county level. In most areas,

STATSGO maps were compiled by generalizing more detailed SSURGO maps.

Where more detailed soil survey maps

were not available, data on geology,

topography, vegetation, and climate were

assembled, together with Land Remote

Sensing Satellite (LANDSAT) images.

Soil of like areas as studied and probable

classification and extent of soils were

determined. STATSGO map units are

combinations of areas on the more

detailed soil maps.

The SSURGO database provides the

most detailed level of information. The

typical map scales are 1:24,000. The

line segments from the original soil survey maps are digitized by the NRCS.

Data for SSURGO is collected and

archived in 7.5-minute topographic

quadrangle units and distributed as a

complete coverage for a soil survey or as

individual quadrangle units within the

survey. The adjoining quadrangles are

edge-matched with the soil survey.

Complexity of the Soils Data

Each STATSGO and SSURGO map

unit can have multiple components,

and each component can have multiple

layers. Attributes of map units are statistical summaries of attributes from

all the component soils used to characterize an entire map unit. Consequently, each map unit can have

multiple components: SURGO a

maximum of three, STATSGO a

maximum of 21, and each component

can have multiple layers (maximum of

six). The Soil Component Attribute

Table maintains 60 variables for each

soil component. The Layer Table

maintains 28 variables for each soil

component layer. In addition to the

soil tables (component and layer),

there is interpretive data.

All STATSGO data is in a digital format; some of the SSURGO data is available in digital format. The challenge is

using this data in GIS. Since the

attribute data is in over 50 tables, the

user must set up numerous links and

relates, decide which layer to look at,

figure out what the results mean, and

then figure out how to use the results

with their own data. SSE shields the user

from the complexity of the soil database

by the use of predefined queries.

Overview of SSE

SSE has four major components: General Soil Queries, Soils Queries to Support

Rangeland Management, Save the Query

Results, plus a download tool for SSURGO data from the NRCS ftp site. Once

SSE has been added to the users ArcView

project, there are just a few additions to

the default ArcView project. There is one

item, Soil Data, which is added to the

menu bar and one tool that is added to

the tool bar. The Soil Data menu contains the link to most of the extension.

The user simply selects the function

desired from the Soil Data menu.

General Soil Queries

Once the user selects one of the General

Soil Queries (either Erodibility,

Field methods

Generalized from more

detailed soil maps, transects, LANDSAT images

1982 National Resources

Inventory

Farm, landowner, and

county natural resource

planning and management.

Regional, State, river

basin, and multi-county

resource planning,

monitoring and management.

National and regional

appraisal, planning, and

monitoring.

SOIL DATABASE PRIMARY USE SCALE SOURCE

SSURGO –

Soil Survey Geographic

STATSGOState Soil Geographic

NATSGONational Soil 

Geographic

1:12,000 to

1:63,360

1:250,000

1:5,000,000

Table 1. NRSC Soil Geographic Databases
Composition, Slope, Soil Water Characteristics, Stability, or Chemistry), there

are a series of easy-to-use menu boxes that

appear. The user simply clicks the check

box to the left of the menu option, and

the query is executed. The results are

displayed in the users current View

where the user is given the option

with each specific menu whether to

use STATSGO or SSURGO data to

execute that query. The user simply

clicks the appropriate box.

An Example

Under Erodibility the user has two

options, Wind Erosion or Water Erosion. If Wind Erosion is selected, a

menu appears (see Table 2, Wind Erosion Query Menu). The user then clicks

on the box for which wind erosion class

s/he wishes to query, the query will run,

and the results will be displayed in

graphic form (see Table 3, Results

from the Wind Query Menu, Baldy

Mountain Allotment).

Rangeland Management

Soil Queries

From the Soil Data menu, if the user

selects the Soils Queries to Support

Rangeland Management, a new menu

will appear. This menu works a little differently from the General Soils Queries

menu, in that with this menu the user

may select multiple queries to run at the

same time. The user clicks the box next

to the query s/he wishes to run then

clicks on the Accept button and those

queries execute. Range queries have predefined choices; for example, which

layer to use, which soil characteristics

to use, depth, etc. A modified query

button is provided so the user can

customize the query.

Help Along the Way

Help is available with this extension in

two ways: (1) a yellow text box display

whenever the mouse crosses some text

on a menu and (2) the on line Users

Guide. The on-line Users Guide is

available from the Internet and from

within ArcView. The Users Guide is

also provided when the extension is

downloaded. It is available in either

Adobe PDF or MS Word.

Saving the Results

Whenever a query is run, the results

are displayed in the users current

View. The results are temporary and

are deleted once the ArcView project

is closed. The user may save the results

very easily with the Save Query

Results option from the Soil Data

menu. The user simply selects the

query results s/he wishes to save from

the Table of Contents and the selects

the Save Query Results from the

menu. The user is asked for a file

name, although a default name is provided, and the user may choose the

location where to save the file. Results

are the available for other uses.

Download SSURGO Data

An easy-to-use download tool has also

been developed with this extension.

There are two ways in which to use this

tool: spatially or alphanumerically. The

difference between the two is whether

or not the user knows the State Soils

Survey Area ID (STSSAID) of the soil

survey needed. If the STSSAID is not

known, the spatial method of download presents the user with a number

of graphics displays depicting the

states, counties, and finally the soil

survey boundaries. The user simply

selects the appropriate responses

from the graphics displays. If the

selected soil survey does exist, the

download will start. Not all soil surveys

are available. If the user knows the

STSSAID of the soil survey needed, the

alphanumeric download option is

available. The user simply enters the

STSSAID and clicks the OK button,

and the download will start.

More Information

More information about SSE is available from the NSTC GIS web page,

http://www.blm.gov/gis/narsc/soils/soil

s.html. The extension documentation

and download are also available from

this web site.

Contact

Mary Beth Stulz

National Science and Technology Center

Denver Federal Center

Building 50, PO Box 25047

Denver, CO, 80225-0047

phone (303) 236-0100

fax (303) 236-3508

email: Mary_Beth_Stulz@blm.gov

Range

Resource Notes are intended to be early

announcements of technical and informational topics for

Bureau of Land Management personnel and some of their customers.

Information in this Resource Note is based on the opinion and

experience of the author and has not been peer-reviewed. Conclusions

and opinions expressed herein do not

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Thank you for your interest in Resource NoteS.

Table 2. Wind Erosion Query Menu

Table 3. Results from the Wind Query Menu,

Baldy Mountain Allotment