Using Web Soil Survey – the Four Steps

Andrew G. Brown, USDA-NRCS Soil Scientist, Sonora, CA.

CALIFORNIA
https://websoilsurvey.sc.egov.usda.gov/

Access digital soils data in four easy steps
1. DEFINE an Area of Interest (AOI)

Draw 

custom AOI

AOI from Soil Survey 

Area / County

You can also import multipart areas from a shapefile!

There are many ways to define your AOI in WSS. 
1. DEFINE an Area of Interest (SoilWeb)

Alternately, you can find your AOI using the SoilWeb Google 

Maps App - just click “Link to WSS” in the top-right corner to 

import the map panel as your AOI.

3. Click ‘Link to WSS’

4. View SoilWeb AOI in 

Web Soil Survey

1. Navigate to UCDavis CA Soil Resource 

Lab Google Maps App 

https://casoilresource.lawr.ucdavis.edu/gmap/ 

2. Open the Menu to 

Zoom To Location
2. VIEW the Soil Map

1. CLICK 

“Soil Map” to 

see your AOI

2. Map is published at 1:24,000 scale 

(you need to specify monitor # of pixels-per-inch)

4. CLICK on links in the Map Unit Legend 

to view individual Map Unit Descriptions

3. Click Legend to toggle 

non-soil layers displayed on 

map (included in final 

report)
3. EXPLORE the Data (Map Unit Descriptions)

What soils occur in 

the map unit?

Minor components:

emphasize landform 

and ecological site 

differences

Where is the map 

unit used?

What it is called?

Major (named) 

components:

• Setting (landform, 

parent material)

• Typical profile 

(horizons, depths, 

texture)

• Properties and 

restrictions

• Interpretive 

classes and 

groups
3. EXPLORE the Data (Suitability / Limitations)

View Rating colors polygons 

with rating classes

View Description describes the 

factors considered in the rating

Add to Shopping Cart (free!)

adds current rating to your 

custom report

EXAMPLE 1. VIEWING A RATING - California (Revised) Storie Index 
Grades 5 and 6:

Very shallow soils on 

wide range of slopes

Grade 3:

Moderately deep soils on 

low slopes (<15%)

Grade 1:

Very deep soils 

on low slopes

Grades 2 and 3:

Deep or moderately deep 

soils (on steeper slopes)

Storie Grade: lower grade is “better” 

(more suited to irrigated ag.)

3. EXPLORE the Data (Suitability / Limitations)

EXAMPLE 1. VIEWING A RATING - California (Revised) Storie Index 
3. EXPLORE the Data (Soil Properties)

COMPONENT AGGREGATION METHODS

• Dominant Condition: apply rating to all 

components; add percentages in each rating 

class; returns rating for most prevalent rating 

class

• Dominant Component: returns rating of 

component with highest percentage

• Weighted-average: apply rating to all 

components; returns the componentpercentage-weighted-average rating

• Minimum or Maximum: apply rating to all 

components; returns the most/least 

limiting/suitable rating

Using Advanced Options, you can change 

the way ratings are generated for Map Units 

that have several soil components

EXAMPLE 2. EXAMPLE 2. ADVANCED COMPONENT AGGREGATION ADVANCED COMPONENT AND HORIZON AGGREGATION
3. EXPLORE the Data (Soil Properties)

EXAMPLE 2 (continued). ADVANCED HORIZON AGGREGATION

ADVANCED OPTIONS

• Component Percent Cutoff: ignore all 

components with percentage less than 

this number 

• Tie-break Rule: In case of a tie when 

determining dominance, return the 

lower or higher rating?

• Interpret Nulls as Zero: Fill in empty 

values with zero? (be careful)

HORIZON AGGREGATION

• Surface layer: only use surface 

horizon?

• All Layers: rate by depth-weightedaverage of all layers in each 

component

• Depth range: Calculate depth-weighted 

average of the layers in range specified 

Also, in Advanced Options you can set rules for excluding 

data/components, as well as averaging horizon data (across depth) 

within components
3. EXPLORE the Data (Soil Properties)

Want to 

return the 

most acidic 

(minimum)

Ignore 

components that 

are less than 15% 

of mapunit

Be “conservative” for ties; lower pH is more acidic; 

in CA630, most soils tend to be at least slightly acidic 

and the lower values will generally be “more limiting” 

Calculate the depth weighted-average pH for each 

component for soil layers within 0-10cm depth interval

GOAL: Show the “most limiting” soil pH in upper 10 cm (4 inches)

EXAMPLE 2 (continued). pH 1:1 water 0-10cm rating
3. EXPLORE the Data (Soil Data Explorer)

In addition to suitability/limitation/property ratings, the 

Soil Data Explorer tab allows you to review basic soil 

science definitions and Ecological Site information.

Also, you can generate independent Soil Reports to 

summarize various classifications, interpretations and 

soil properties in a tabular format.
1. Set report subtitle and 

output size

2. Check Table of Contents

(note items added under 

Soil Data Explorer section)

3. Check Out 

(top right corner of WSS window)!

4. View or print PDF output

4. CHECK OUT (make custom resource report)
Optional: Skipping the AOI

For GIS/external use -- directly download 

SSURGO data in .ZIP format via 

‘Download Soils Data’ tab

– No need to specify AOI 

– Search soil surveys by State/County

– Tabular data delivered as MS Access database

– Spatial layers delivered as shapefile