Premise
SSURGO is a digital, high-resolution (1:24,000), soil survey database produced by the USDA-NRCS. It is one of the largest and most complete spatial databases in the world; and is available for nearly the entire USA at no cost. These data are distributed as a combination of geographic and text data, representing soil map units and their associated properties. Unfortunately the text files do not come with column headers, so a template is required to make sense of the data. Alternatively, one can use an MS Access template to attach column names, generate reports, and other such tasks. CSV file can be exported from the MS Access database for further use. A follow-up post with text file headers, and complete PostgreSQL database schema will contain details on implementing a SSURGO database without using MS Access.

If you happen to have some of the SSURGO tabular data that includes column names, the following R code may be of general interest for resolving the 1:many:many hierarchy of relationships required to make a thematic map.

 
This is the format we want the data to be in

    mukey     clay      silt      sand water_storage
   458581 20.93750 20.832237 20.861842     14.460000
   458584 43.11513 30.184868 26.700000     23.490000
   458593 50.00000 27.900000 22.100000     22.800000
   458595 34.04605 14.867763 11.776974     18.900000

 
So we can make a map like this

Rapid urban and sub-urban expansion in the San Joaquin Valley have resulted in the loss of millions of acres of prime farmland in the last 100 years. Approximately 11% of class 1 (irrigated) land and 7% of class 2 land have already been paved over in the Fresno-Madera region (first image below). Recent projections in the expansion of urban areas in this region suggests that by 2085 an additional 28% of class 1 and 25% of class 2 land will be paved over (second image below). This is a preliminary summary-- details to follow.

Fresno Area Urban Areas vs Irrigated LCC: grey regions are current urban areas

 
Just Checking

-- NAD27 to NAD83 
echo 119d7\'4\"W 36d23\'13\"N | cs2cs +proj=latlong +datum=NAD27 +to +proj=latlong +datum=NAD83 -f "%.6f"
  

Background and Justification

 
Premise

Compute a series of weighted-average soil texture fractions (sand, silt, clay), for every component, of every map unit in Yolo County. These values will be further weighted by the spatial distribution of each map unit.

 
EEMT Calculation from MAP and MAAT [See Rasmussen & Tabor; SSSAJ 71: 1719 - 1729]

 
Overview:

 
Selection, Filtering and Sorting

• Selecting a summary of horizon thickness, sand, silt, clay and AWC for a given component (chorizon table).
  

 
Overview

You should include a search method that uses APNs.