soilDB (version 2.3)

SDA_query: Soil Data Access Query

Description

Submit a query to the Soil Data Acccess (SDA) website in SQL, get the results as a dataframe.

Usage

SDA_query(q)

Arguments

q

a valid T-SQL query surrounded by double quotes

Value

A dataframe containing the results. NULL is retutned when queries result in 0 matches rows.

Details

The SDA website can be found at http://sdmdataaccess.nrcs.usda.gov and query examples can be found at http://sdmdataaccess.nrcs.usda.gov/QueryHelp.aspx. A library of query examples can be found at https://nasis.sc.egov.usda.gov/NasisReportsWebSite/limsreport.aspx?report_name=SDA-SQL_Library_Home.

SSURGO (detailed soil survey) and STATSGO (generalized soil survey) data are stored together within SDA. This means that queries that don't specify an area symbol may result in a mixture of SSURGO and STATSGO records. See the examples below and the SDA Tutorial for details.

See Also

mapunit_geom_by_ll_bbox

Examples

# NOT RUN {

## get SSURGO export date for all soil survey areas in California
# there is no need to filter STATSGO 
# because we are filtering on SSURGO areasymbols
q <- "SELECT areasymbol, saverest FROM sacatalog WHERE areasymbol LIKE 'CA%';"
x <- SDA_query(q)
head(x)


## get SSURGO component data associated with the 
## Amador series / major component only
# this query must explicitly filter out STATSGO data
q <- "SELECT cokey, compname, comppct_r 
FROM legend
INNER JOIN mapunit mu ON mu.lkey = legend.lkey
INNER JOIN component co ON mu.mukey = co.mukey 
WHERE 
-- critical: filter out STATSGO data
legend.areasymbol != 'US'
AND compname = 'Amador' ;"

res <- SDA_query(q)
str(res)


## get component-level data for a specific soil survey area (Yolo county, CA)
# there is no need to filter STATSGO because the query contains
# an implicit selection of SSURGO data by areasymbol
q <- "SELECT 
component.mukey, cokey, comppct_r, compname, taxclname, 
taxorder, taxsuborder, taxgrtgroup, taxsubgrp
FROM legend
INNER JOIN mapunit ON mapunit.lkey = legend.lkey
LEFT OUTER JOIN component ON component.mukey = mapunit.mukey
WHERE legend.areasymbol = 'CA113' ;"

res <- SDA_query(q)
str(res)


## get tabular data based on result from spatial query
# there is no need to filter STATSGO because
# SDA_Get_Mukey_from_intersection_with_WktWgs84() implies SSURGO
#
# requires raster and rgeos packages because
library(raster) # suggested by soilDB
library(rgeos)  # additional

# text -> bbox -> WKT
# xmin, xmax, ymin, ymax
b <- c(-120.9, -120.8, 37.7, 37.8)
p <- writeWKT(as(extent(b), 'SpatialPolygons'))
q <- paste0("SELECT mukey, cokey, compname, comppct_r
            FROM component 
            WHERE mukey IN (
            SELECT DISTINCT mukey 
            FROM SDA_Get_Mukey_from_intersection_with_WktWgs84('", p, "') 
            )
            ORDER BY mukey, cokey, comppct_r DESC")

x <- SDA_query(q)
str(x)
# }
# NOT RUN {


# }