SSURGO Data Packaging and Use 

November 2012 

United States Department of Agriculture 

Natural Resources Conservation Service 

Table of Contents 

INTRODUCTION ........................................................................................................................................ 5

SSURGO EXPORT PACKAGING ............................................................................................................ 6

CONTENTS OF DIRECTORY “SOIL_SSASYMBOL” ......................................................................................... 6

CONTENTS OF DIRECTORY “TABULAR” ...................................................................................................... 7

CONTENTS OF DIRECTORY “SPATIAL” ........................................................................................................ 7

Non-Spatial Attributes Embedded in the Spatial Data .......................................................................... 9

DATA VERSIONING ................................................................................................................................ 10

LOCATING VERSION INFORMATION .......................................................................................................... 10

MAKING SURE THE TABULAR DATA VERSION IS COMPATIBLE WITH THE SPATIAL DATA VERSION ......... 11

USING SOIL TABULAR DATA .............................................................................................................. 12

USING A SSURGO TEMPLATE DATABASE ............................................................................................... 13

USING SOIL SPATIAL DATA ................................................................................................................ 13

PERSONAL GEODATABASE ....................................................................................................................... 14

THE CHALLENGE OF USING SOIL DATA IN A GIS ..................................................................................... 15

Thematic Map Generation .................................................................................................................. 15

Methods of Aggregation ...................................................................................................................... 15

Dominant Component ..................................................................................................................................... 17

Dominant Condition ........................................................................................................................................ 18

Most Limiting ................................................................................................................................................. 18

Least Limiting ................................................................................................................................................. 19

Weighted Average ........................................................................................................................................... 19

All Components .............................................................................................................................................. 20

Presence/Absence ............................................................................................................................................ 21

Soil Data Viewer Application ............................................................................................................. 21

CONTACTING SUPPORT ....................................................................................................................... 22

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Introduction 

Soil survey data can be downloaded from the Soil Data Mart: 

http://soildatamart.nrcs.usda.gov

Data for a soil survey area includes a tabular component and a spatial component. The tabular 

component is typically imported into a database for querying, reporting and analysis. The spatial 

component is typically viewed and analyzed using a Geographic Information System (GIS). 

Although a finished soil survey area always includes both components, a survey area’s tabular 

component may be available in the Soil Data Mart long before the corresponding spatial 

component. A soil survey area’s tabular component can be downloaded independent of its 

corresponding spatial component, and vice versa. A survey area cannot be posted to the Soil 

Data Mart until its tabular component is available. Therefore there will never be a soil survey 

area in the Soil Data Mart for which only the spatial component is available. 

Data from the Soil Data Mart is distributed in what is referred to as “SSURGO” format. For the 

tabular component, this format dictates which soil attributes are included, how those attributes 

are defined, how those attributes are grouped and how those groups are related. For the spatial 

component, this format dictates which spatial layers are defined, which spatial layers are 

mandatory and the standards to which that spatial data conforms. 

The SSURGO format has evolved over time. There have been two major versions and four 

minor versions. The major differences between these versions are summarized below. 

SSURGO 

Version 

Date Description 

1.0 circa 1990? The format of the tabular component is based on the State Soil 

Survey database (SSSD), the precursor to NASIS (National Soil 

Information System). 

2.0 January 

2001 

The format of the tabular component is based on the NASIS 

database. 

2.1 December 

2003 

The format of the tabular and spatial component is modified in 

order to support more explicit versioning of soil survey data. This 

format became available with the advent of the Soil Data Mart. 

2.2 October 

2005 

The format of the tabular component is modified to include the data 

necessary to drive the Soil Data Viewer application. 
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Document Version: 6 Page: 6 of 22 

SSURGO Export Packaging 

When soil data is exported from the Soil Data Mart, the end result is always a single zip file, 

regardless of what export options were selected. The format of an export file name is: 

soil_ssasymbol.zip, where ssasymbol is the symbol of the corresponding soil survey area. A soil 

survey area symbol uniquely identifies a soil survey area. An export from the Soil Data Mart 

always contains data for one and only one soil survey area. 

A survey area symbol is a five character string where the first two characters are a U.S. state or 

territory postal code, and the last three characters are digits that represent the soil survey area 

within the corresponding state or territory. 

A SSURGO export file can be unzipped using WinZip or an equivalent application. When an 

export file is unzipped, the following directory hierarchy is produced in the directory to which 

the export file was unzipped: 

soil_ssasymbol

 tabular 

 spatial 

where ssasymbol is the symbol of the corresponding soil survey area. 

Contents of Directory “soil_ssasymbol” 

In addition to subdirectories “tabular” and “spatial”, this directory contains either three or four 

files: 

1. soil_metadata_ssasymbol.txt 

2. soil_metadata_ssasymbol.xml 

3. readme.txt 

4. something.zip (optional) 

The first two files contain the FGDC metadata for the corresponding survey area, in plain ASCII 

and XML format, respectively. FGDC is the acronym for Federal Geographic Data Committee. 

The FGDC metadata primarily pertains to spatial soil data. A smaller portion of the FGDC 

metadata pertains to the tabular soil data. 

File “readme.txt” contains a lot of the same information that is presented in this document. The 

top of this file documents the versions of the data included in the export, as well as any options 

that were specified if spatial data was included in the export. 
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File “something.zip”, if it exists, is a zipped Microsoft Access database, into which the tabular 

soil data can be imported. This file will only exist if the person who generated this export 

requested its inclusion. The embedded Microsoft Access database is referred to as a “SSURGO 

template database”. There is more than one SSURGO template database, so the root portion of 

the file name can vary. SSURGO template databases are discussed in the section titled “Using 

Soil Tabular Data”. 

If a SSURGO template database was not included in the export, one can always be downloaded 

from the following Soil Data Mart web page: 

http://soildatamart.nrcs.usda.gov/Templates.aspx

Contents of Directory “tabular” 

Directory “tabular” contains a set of ASCII field and text delimited files. Fields are delimited by 

the pipe or vertical bar character. Text fields are double quote delimited because such a field can 

contain embedded field delimiters and/or line ends. Within a text field, any embedded double 

quotes are doubled. 

With the exception of “version.txt”, each of these files corresponds to a table in a SSURGO 

template database. Which ASCII delimited file (“Import/Export File Name”) corresponds to 

which database table (“Table Physical Name”) is documented in the “SSURGO Metadata – 

Tables” report. This report is available at http://soildatamart.nrcs.usda.gov/ssurgometadata.aspx. 

File “version.txt” records the SSURGO version of the corresponding tabular data. The content 

of this file is checked when tabular data is imported into a SSURGO template database. 

Contents of Directory “spatial” 

The exact content of directory “spatial” depends on the spatial format option that was selected 

when the export was generated. Spatial data can be exported in any of the following formats: 

1. ESRI Shape File 

2. ArcInfo Coverage 

3. ArcInfo Interchange 

In addition to specifying a spatial format, a user exporting soil spatial data from the Soil Data 

Mart can specify a coordinate system and projection. When spatial data is included in an export, 

the corresponding spatial format and coordinate system are documented in the “readme.txt” file, 

located in the root directory that was created by unzipping the export file. The export spatial 
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format and coordinate system are also documented in the FGDC metadata, also located in the 

root directory that was created by unzipping the export file. 

In discussing the spatial data, it helps to separate the logical from the physical. The possible 

logical spatial entities are: 

1. Soil Survey Area Boundary Polygon(s) (Required) 

2. Map Unit Boundary Polygons (Required) 

3. Line Map Units (Optional) 

4. Point Map Units (Optional) 

5. Line Spot Features (Optional) 

6. Point Spot Features (Optional) 

7. Spot Feature Descriptions (Required if Line Spot Features or Point Spot Features are 

included) 

Each of the first six spatial entities represent what is referred to as a “feature class”. The last 

entity, Spot Feature Descriptions, is an ASCII field and text delimited file that contains narrative 

descriptions of any corresponding line or point spot features. In effect, this is “tabular data” that 

is considered to be part of the spatial data. 

“Required” means that, if spatial data for the corresponding survey area exists, this data must be 

included. In other words, if spatial data exists, at a minimum, a soil survey area boundary 

polygon feature class and a map unit boundary polygon feature class will exist. 

A single logical spatial entity is delivered as multiple files, sometimes with one or more 

subdirectories, depending on the spatial format that was selected when the export was generated. 

Some, but not necessarily all, of the files corresponding to a particular logical spatial entity have 

a name whose prefix denotes the corresponding spatial entity. 

For spatial data in ESRI Shape File format, the following file name prefixes are used: 

File Name Prefix Spatial Entity 

soilsa_a soil survey area boundary polygon(s) 

soilmu_a map unit boundary polygons 

soilmu_l line map units 

soilmu_p point map units 

soilsf_l line spot features 

soilsf_p point spot features 

soilsf_t spot feature descriptions 
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For spatial data in ArcInfo Coverage or ArcInfo Interchange format, the following file name 

prefixes are used: 

File Name Prefix Spatial Entity 

ssa_a soil survey area boundary polygon(s) 

smu_a map unit boundary polygons 

smu_l line map units 

smu_p point map units 

ssf_l line spot features 

ssf_p point spot features 

ssf_t spot feature descriptions 

Non-Spatial Attributes Embedded in the Spatial Data 

A handful of non-spatial (non-geometry) attributes are embedded into the various spatial feature 

classes. These attributes either: (1) logically identify a corresponding tabular entity, (2) serve as 

the physical link to the corresponding tabular entity, or (3) identify the corresponding spatial data 

version. See the section titled “Data Versioning” for more information about data versioning. 

Attribute Present in the Following 

Spatial Feature Classes or 

Files 

Purpose 

Survey Area Symbol 

(column name is always 

“areasymbol”) 

All Logically identifies the 

corresponding survey area. 

Spatial Data Version 

(column name is either 

“spatialversion” or 

“spatialver” – for some 

spatial formats, column 

names are limited to no 

more than ten characters) 

All Logically identifies the 

corresponding spatial data 

version. 

Legend Key (column name 

is always “lkey”) 

Survey Area Boundary 

Polygon(s) 

Links survey area boundary 

spatial record to the 

corresponding legend table 

record. 

Map Unit Symbol (column 

name is always “musym”) 

Map Unit Boundary 

Polygons, Line Map Units, 

Point Map Units 

Logically identifies the 

corresponding map unit. 

Map Unit Key (column 

name is always “mukey”) 

Map Unit Boundary 

Polygons, Line Map Units, 

Point Map Units 

Links map unit boundary 

spatial record to the 

corresponding mapunit 

table record. 

Spot Feature Symbol Line Spot Features, Point Logically identifies the 
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(column name is always 

“featsym”) 

Spot Features, Spot Feature 

Descriptions File 

corresponding spot feature. 

Spot Feature Key (column 

name is always “featkey”) 

Line Spot Features, Point 

Spot Features, Spot Feature 

Descriptions File 

Links spot feature spatial 

record to corresponding 

feature description record. 

Data Versioning 

With the advent of the Soil Data Mart, data for a soil survey area is now explicitly versioned. 

There are three different versions: 

1. Survey Area Version 

2. Tabular Data Version 

3. Spatial Data Version 

Since tabular soil data for a survey area can be updated without updating the corresponding 

spatial soil data, and vice versa, tabular data and spatial data are versioned independently of one 

another. For a survey area, any new Tabular Data Version or Spatial Data Version results in a 

new Survey Area Version. 

For any version, there are two version attributes: 

1. Version Number (usually referred to as “version”) 

2. Version Established Date and Time 

Version numbers are serially incremented integer values, starting at one. 

Locating Version Information 

Survey area version information can be found in the following locations: 

1. In the readme.txt file, located in the root directory that was created by unzipping the 

export file. 

2. If tabular data is included in the export, in the sacatalog table record for the 

corresponding survey area (file sacatlog.txt or table sacatalog when that tabular data has 

been imported into a SSURGO template database). 
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3. In the page footer of soil reports in the MS Access SSURGO template database, when 

tabular data is included in the export and that tabular data has been imported into a 

SSURGO template database. 

4. In soil report “Survey Area Data Summary” in the MS Access SSURGO template 

database, when tabular data is included in the export and that tabular data has been 

imported into a SSURGO template database. 

Tabular data version information can be found in the following locations: 

1. In the readme.txt file, located in the root directory that was created by unzipping the 

export file, when tabular data is included in the export. 

2. If tabular data is included in the export, in the sacatalog table record for the 

corresponding survey area (file sacatlog.txt or table sacatalog when that tabular data has 

been imported into a SSURGO template database). 

3. In the body of soil report “Survey Area Data Summary” in the MS Access SSURGO 

template database, when tabular data is included in the export and that tabular data has 

been imported into a SSURGO template database. 

Spatial data version information can be found in the following locations: 

1. In the readme.txt file, located in the root directory that was created by unzipping the 

export file, when spatial data is included in the export. 

2. Embedded in spatial data for any spatial feature class, when spatial data is included in 

the export. 

Making Sure the Tabular Data Version is compatible with the 

Spatial Data Version 

Soil tabular and spatial data are compatible when: 

1. For every survey area polygon feature, there is a corresponding legend table record. 

All survey area features with the same area symbol share the same legend table record. 

2. For every map unit polygon, line or point feature, there is a corresponding mapunit 

table record. All map unit features with the same map unit symbol share the same 

mapunit table record. 

Every mapunit table record IS NOT required to have a corresponding map unit feature. While 

this is rare, it is permitted. The case for which this exception is permitted is for a survey area in 

the process of being mapped, where the spatial data is not yet complete. 
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If the export file includes both tabular and spatial data, that tabular data is compatible with that 

spatial data. Where things can get out of sync is when tabular data is obtained independently of 

its corresponding spatial data, or vice versa. 

On your PC there is no easy way to verify if a set of tabular and spatial data are compatible. The 

most reliable way to verify compatibility is to visit the Soil Data Mart, access the Download 

page for the survey area in question, and look at the tabular and spatial version numbers 

displayed on the Download page. If your version numbers don’t match the version numbers 

displayed on the Download page, you should request a new export that includes both tabular and 

spatial data. 

Using Soil Tabular Data 

The tabular data as delivered in a SSURGO export file isn’t very usable as is. The tabular data is 

distributed between approximately sixty ASCII delimited files. In order to effectively use this 

data, it needs to be imported into a database. Even after loading data into a database, you still 

need to understand what the tables and attributes represent, how tables are related and what data 

constraints are in place. This type of information is available on the following web page: 

http://soildatamart.nrcs.usda.gov/ssurgometadata.aspx

The above URL is also the location of this document. 

At the current time we provide a Microsoft Access database into which soil tabular data can be 

imported. We refer to this database as a “SSURGO template database”. In order to use this 

database, you have to have Microsoft Access installed on your PC. 

In a SSURGO template database, the SSURGO database structure has already been created. 

Tabular soil data can be imported by running a macro that resides in the database. Once data has 

been imported, a variety of reports can be generated. If you are willing to learn a little bit about 

Microsoft Access, you can create your own queries against the data you have imported. 

If a SSURGO template database was included with the exported data, it will be the only zipped 

file in the root directory that was created by unzipping the export. If a SSURGO template 

database was not included with the exported data, one can be downloaded from the following 

location: 

http://soildatamart.nrcs.usda.gov/templates.aspx

A number of different SSURGO template databases are typically available. A national SSURGO 

template database serves as the default. For a national SSURGO template database, the 

corresponding “state code” in the template database web page data grid is “US”. 
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Some states have created a customized SSURGO template database for their state. If a 

customized SSURGO template database is available for the state in whose data you are 

interested, you should use that state’s customized SSURGO template database in lieu of the 

national SSURGO template database. 

When selecting a SSURGO template database, if possible, select one whose MS Access version 

is the same as the version of MS Access that you have installed on your PC. At the current time, 

national SSURGO template databases are available for Access 97, Access 2000 and Access 

2002/2003. What MS Access versions are supported for a state customized SSURGO template 

database varies from state to state. While you can convert a SSURGO template database from 

one version of MS Access to another, this conversion is not always successful. 

At the current time, we do not support the use of any database other than MS Access. If you are 

interested in loading soil tabular data into a database other than MS Access, and have questions, 

please contact the NASIS Hotline. See the section titled “Contacting Support” for the details. 

Using a SSURGO Template Database 

For information about importing tabular data into a template database, or information about the 

capabilities of the SSURGO template database in general, do the following: 

1. Open the MS Access SSURGO template database in the appropriate version of MS Access. 

2. Click the Reports tab of the Database Window. The Database Window may be behind a form 

titled “SSURGO Import” or “Soil Reports”. 

3. Either double-click the report titled "How to Understand and Use this Database", or select this 

report and then click "Preview". 

4. After the Report Viewer window is displayed, either click the printer icon or select "Print" 

from the File menu. You can also browse this report using the Preview window. 

Using Soil Spatial Data 

The spatial data can’t be used until it has been imported into a GIS. In order to import soil 

spatial data into a GIS, the GIS must be able to import one of the following spatial formats: 

1. ESRI Shape File 

2. ArcInfo Coverage 

3. ArcInfo Interchange 
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Obviously the spatial data isn’t of much use unless the corresponding tabular data is also 

available. Once you have successfully imported the soil tabular data into a database, and have 

also successfully imported soil spatial data into a GIS, it’s pretty much uphill from there. See the 

subsection titled “The Challenge of Using Soil Data in a GIS” for more details. 

Personal Geodatabase 

If spatial data is available for the survey in which you are interested, and if you have access to 

ArcGIS, a personal geodatabase can be created. To do this, import the tabular data into a 

SSURGO template database in the usual way, and then use ArcCatalog to import each of the 

spatial data feature classes into that same SSURGO template database. The spatial data to be 

imported must be in either Shape File or Coverage format. The resulting personal geodatabase 

can be used with ArcGIS or ArcView 8 or later. 

The personal geodatabase doesn’t know what tables are related unless you explicitly create 

relationship classes to indicate how two tables are related. If you want to establish relationship 

classes to any of the tabular data tables, you must register (“register to the personal 

geodatabase”) each of the tabular tables of concern. The relationships between all SSURGO 

tables are documented in the SSURGO data model diagrams, which can be found at: 

http://soildatamart.nrcs.usda.gov/ssurgometadata.aspx

If you create a personal geodatabase and want to be able to link to spot feature descriptions, the 

spot feature descriptions must be explicitly imported into the SSURGO template database, but 

keep in mind that a survey area may or may not include spot features. Spot feature descriptions, 

when they exist, are bundled and versioned with the spatial data, but the spot feature descriptions

are not a feature class. To import spot feature descriptions into a SSURGO template database, 

run the macro titled “Import Feature Descriptions”. This macro will import spot feature 

descriptions into the table named “featdesc”. The macro displays a dialog box that prompts for 

the fully qualified path of the file containing the spot feature descriptions. This file, if it exists, 

resides in the subdirectory named “spatial”, and the name of the file containing the spot feature 

descriptions starts with “soilsf_t” or “ssf_t” for Shape File format or Coverage format, 

respectively. This file has a “.txt” extension. 

One last thing to keep in mind is the size limit of an MS Access database, which is 1 gigabyte for 

Access 97, and 2 gigabytes for Access 2000 and later versions. The amount of space required 

for a given survey area’s tabular and spatial data varies widely. You may or may not be able to 

create a personal geodatabase that includes data for more than one survey area, depending on the 

size of the survey areas involved. For a single very large survey area, you may be able to create 

a personal geodatabase, but performance may be degraded. 
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The Challenge of Using Soil Data in a GIS 

For compatible tabular and spatial data, the relationship between the tabular and spatial data has 

already been established before that data was ever exported from the Soil Data Mart. You are 

not responsible for establishing this relationship. (For information about tabular and spatial data 

compatibility, see the section titled “Making Sure the Tabular Data Version is compatible with 

the Spatial Data Version”. For information about how the tabular and spatial data are linked, see 

the section titled “Non-Spatial Attributes Embedded in the Spatial Data”.) 

The challenge of using soil data in a GIS is due to the following: 

1. Thematic maps must be based on map units. 

2. The vast majority of attributes used to create a thematic map are not attributes of a 

map unit but attributes of an entity that repeats for its corresponding map unit. 

Thematic Map Generation 

Thematic maps are a representation of reality and can only display a small part of that reality in a 

single map. Information on the map is typically for a single theme. 

Polygons in the digital map data are map unit delineations. Therefore, themes for thematic maps 

are based on map units. Many map polygons can be labeled the same, but all point to the same 

record in the map unit table. 

Map units are typically made up of one or more named soils. Other miscellaneous land types or 

areas of water may be included. These entities and their percent compositions make up the map 

unit components and define the map unit composition. Soil components are typically composed 

of multiple horizons (layers). Component attributes must be aggregated to a map unit level for 

map visualization. Horizon attributes must be aggregated to the component level, before 

components are aggregated to the map unit level. Horizon attributes may be aggregated for the 

entire soil profile or for a specific depth range. One may only be interested in the value of a 

horizon attribute for the surface layer. 

Methods of Aggregation 

There are a number of options for aggregating data to the map unit level. The various options 

will be illustrated using selected columns from the “component” and “chorizon” tables. These 

tables and columns are described in reports “SSURGO Metadata - Tables” and “SSURGO 

Metadata - Table Column Descriptions”. These reports are available at 

http://soildatamart.nrcs.usda.gov/ssurgometadata.aspx. 
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In SSURGO data, the field “mukey” uniquely identifies a map unit, and the field “cokey” 

uniquely identifies a map unit component. 

Table: component 

mukey 

(Map 

Unit 

Key) 

cokey 

(Component Key) 

comppct_r 

(Representative 

Percent 

Composition) 

corcon 

(Corrosion 

Concrete) 

hydricrating 

(Hydric 

Rating) 

100017 100017:149541 60 low yes 

100017 100017:149542 40 high yes 

 

100049 100049:149613 50 low yes 

100049 100049:149614 50 moderate no 

147626 147626:215195 35 moderate no 

147626 147626:215196 25 low no 

147626 147626:215197 20 low no 
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Table: chorizon 

cokey 

(Component Key) 

hzdept_r 

(Representative 

Horizon Depth to 

Top) 

hzdepb_r 

(Representative 

Horizon Depth to 

Bottom) 

claytotal_r 

(Representative Clay 

Total Separate) 

100017:149541 0 20 9.5 

100017:149541 20 76 12.5 

100017:149541 76 152 1.5 

 

100017:149542 0 20 9.5 

100017:149542 20 30 11.5 

100017:149542 30 152 3.5 

 

100049:149613 0 76 6.0 

100049:149613 76 152 6.0 

100049:149614 0 36 6.5 

100049:149614 36 152 4.5 

147626:215195 0 10 12.0 

147626:215195 10 41 7.0 

147626:215195 41 51 

 

147626:215196 0 3 33.5 

147626:215196 3 13 36.0 

147626:215196 13 41 42.5 

147626:215196 41 152 

 

147626:215197 0 8 22.5 

147626:215197 8 41 22.5 

147626:215197 41 46 26.5 

147626:215197 46 152 

Dominant Component 

The interpretation rating class or soil property value of the component with the largest percent 

composition is used to class the map unit. If there is more than one component that shares the 

highest percent composition, a “tie-break rule” indicates which value should be selected. 

For this example, in the case of a tie on percent composition, we’ll choose the more restrictive 

value. The results for Dominant Component for Corrosion Concrete are shown below. 
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mukey comppct_r corcon 

100017 60 low 

 

100049 50 moderate 

(more restrictive value was 

returned for the tie) 

 

147626 35 moderate 

Dominant Condition 

For the components in each map unit, like interpretation rating classes or soil property values are 

grouped, and their corresponding percent compositions are summed. The interpretation rating 

class or soil property value for the group with the largest percent composition is used to class the 

map unit. If there is more than one group that shares the highest percent composition, a “tiebreak rule” indicates which value should be selected. 

For this example, in the case of a tie on percent composition, we’ll choose the more restrictive 

value. The results for Dominant Condition for Corrosion Concrete are shown below. 

mukey comppct_r corcon 

100017 60 low 

 

100049 50 moderate 

(more restrictive value was 

returned for the tie) 

 

147626 45 (25/low + 20/low) low 

Most Limiting 

The most limiting interpretation rating class for all of the components in a map unit is used to 

class the map unit. This aggregation method is limited to interpretive type attributes where 

which end of the spectrum is considered most limiting is already established. 

The results for Most Limiting for Corrosion Concrete are shown below. 
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Document Version: 6 Page: 19 of 22 

mukey corcon 

100017 high 

 

100049 moderate 

147626 moderate 

Least Limiting 

The least limiting interpretation rating class for all of the components in a map unit is used to 

class the map unit. This aggregation method is limited to interpretive type attributes where 

which end of the spectrum is considered least limiting is already established. 

The results for Least Limiting for Corrosion Concrete are shown below. 

mukey corcon 

100017 low 

 

100049 low 

147626 low 

Weighted Average 

A weighted average of the soil property value for all components in the map unit is used to class 

the map unit. Percent composition is used as the weighting factor. Obviously this aggregation 

method is only suitable for numeric attributes. 

If the soil property being aggregated is an attribute of a soil horizon, for each component, a 

single value for all included horizons must be determined before computing a weighted average 

for all components. In this case, the single component value is also computed as a weighted 

average, where the weighting factor for each horizon is its percent of the depth range in question. 

For this example, let’s derive a weighted average value for total clay in the upper 50 centimeters 

of the soil. 

Step 1 – For each component, compute a weighted average value for total clay in the upper 50 

centimeters of the soil. Where soil depth is less than 50 cm, use whatever lowest depth is 

available. 

Total Clay in the Upper 50 cm (or less) = ∑ (horizon thickness/total thickness*total clay) for all 

included soil horizons 
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cokey comppct_r Total Clay in the Upper 50 cm (or less) 

100017:149541 60 20/50*9.5 + 30/50*12.5 = 11.3 

100017:149542 40 20/50*9.5 + 10/50*11.5 + 20/50*3.5 = 7.5 

 

100049:149613 50 50/50*6.0 = 6.0 

100049:149614 50 36/50*6.5 + 14/50*4.5 = 5.94 

 

147626:215195 35 10/41*12.0 + 31/41*7.0 = 8.22 

(no clay data was available below 41 cm) 

147626:215196 25 3/41*33.5 + 10/41*36.0 + 28/41*42.5 = 40.26 

(no clay data was available below 41 cm) 

147626:215197 20 8/46*22.5 + 33/46*22.5 + 5/46*26.5 = 22.93 

(no clay data was available below 46 cm) 

Step 2 – For each map unit, compute a weighted average value for total clay in the upper 50 

centimeters (or less) of the soil. 

Total Clay in the Upper 50 cm (or less) = ∑ (percent composition* Total Clay in the Upper 50 

cm (or less)) for all components in the map unit 

mukey Total Clay in the Upper 50 cm (or less) 

100017 (60/100*11.3) + (40/100*7.5) = 9.78 

 

100049 (50/100*6.0) + (50/100*5.94) = 5.97 

 

147626 (35/80*8.22) + (25/80*40.26) + (20/80*22.93) = 21.91 

All Components 

The highest or lowest soil property value for all of the components in a map unit is used to class 

the map unit. 

The results for All Components for Highest Total Clay in the Surface Layer are shown below. 

mukey claytotal_r 

100017 9.5 

 

100049 12.0 

147626 33.5 
SSURGO Data Packaging and Use 

Document Version: 6 Page: 21 of 22 

Presence/Absence 

All of the components in a map unit are evaluated as to whether a certain condition is present or 

absent, and the map unit is then assigned one of the following four classes: 

1. Presence or absence of condition is always known, and condition is present for all 

components. 

2. Presence or absence of condition is always known, and condition is never present for 

any component. 

3. Presence or absence of condition is not always known, but condition is present for 

some components. 

4. Presence or absence of condition is not always known, but condition was not present 

for any component for which the condition was known. 

The result classes may be assigned names more specific to the condition in question. 

The results for Presence/Absence of Hydric Components are shown below. 

mukey Hydric Components 

100017 All Hydric 

 

100049 Partially Hydric 

147626 All Not Hydric 

Soil Data Viewer Application 

The examples above represent relatively simple cases. Dealing with missing data or missing 

percent composition hasn’t been addressed. None of the examples deal with attributes that don’t 

have a one to one relationship with either a component or soil horizon. To be able to 

dynamically perform aggregation for large volumes of data, for a variety of attributes, in 

anything resembling real time, requires considerable programming. The functionality provided 

by commercial applications like Microsoft Access or ESRI’s GIS products don’t help much 

when it comes to aggregation. 

The NRCS solution to this problem was to create an application that does the most commonly 

needed aggregations on demand. This application is known as “Soil Data Viewer”. 

Here is the description of the Soil Data Viewer application from the Soil Data Viewer User 

Guide: 
SSURGO Data Packaging and Use 

Document Version: 6 Page: 22 of 22 

Soil Data Viewer is a tool built as an extension to ArcMap that allows a user to create 

soil-based thematic maps. The application can also be run independent of ArcMap, but 

output is then limited to a tabular report. 

The soil survey attribute database associated with the spatial soil map is a complicated 

database with more than 50 tables. Soil Data Viewer provides users access to soil 

interpretations and soil properties while shielding them from the complexity of the soil 

database. Each soil map unit, typically a set of polygons, may contain multiple soil 

components that have different use and management. Soil Data Viewer makes it easy to 

compute a single value for a map unit and display results, relieving the user from the 

burden of querying the database, processing the data and linking to the spatial map. 

Soil Data Viewer contains processing rules to enforce appropriate use of the data. This 

provides the user with a tool for quick geospatial analysis of soil data for use in resource 

assessment and management. 

To see which version of Soil Data Viewer is compatible with which version of ArcGIS (ArcMap 

is a component of ArcGIS), please visit: 

http://soildataviewer.nrcs.usda.gov/download.aspx

Additional software requirements are listed on the download page that corresponds to a 

particular version of Soil Data Viewer. 

For additional information about the capabilities of a particular version of Soil Data Viewer, 

please visit: 

http://soildataviewer.nrcs.usda.gov/userguide.aspx

Contacting Support 

Questions should be directed to the National Soil Information System (NASIS) Hotline. The 

NASIS Hotline, which resides at the USDA NRCS National Soil Survey Center in Lincoln 

Nebraska, is staffed from 8:00 AM to 4:30 PM Central Time. 

(402) 437-5378 – Steve Speidel 

(402) 437-5379 – Tammy Cheever 

e-mail: hotline@lin.usda.gov