Submit a query to the Soil Data Access (SDA) REST/JSON web-service and return the results as a data.frame. There is a 100,000 record limit and 32Mb JSON serializer limit, per query. Queries should contain a WHERE statement or JOIN condition to limit the number of rows affected / returned. Consider wrapping calls to SDA_query in a function that can iterate over logical chunks (e.g. areasymbol, mukey, cokey, etc.). The function makeChunks can help with such iteration.
Details
The SDA website can be found at https://sdmdataaccess.nrcs.usda.gov and query examples can be found at https://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.
Examples
# \donttest{
## get SSURGO export date for all soil survey areas in California
# there is no need to filter STATSGO
# because we are filtering on SSURGO area symbols
q <- "SELECT areasymbol, saverest FROM sacatalog WHERE areasymbol LIKE 'CA%';"
x <- SDA_query(q)
#> single result set, returning a data.frame
head(x)
#> areasymbol saverest
#> 1 CA011 8/28/2023 9:44:47 PM
#> 2 CA013 9/12/2023 8:16:32 PM
#> 3 CA021 9/6/2023 8:39:55 PM
#> 4 CA031 8/31/2023 10:37:14 PM
#> 5 CA033 8/28/2023 9:47:32 PM
#> 6 CA041 9/11/2023 11:41:42 PM
## 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 legend.areasymbol != 'US' AND compname = 'Amador';"
res <- SDA_query(q)
#> single result set, returning a data.frame
str(res)
#> 'data.frame': 54 obs. of 3 variables:
#> $ cokey : int 24044962 24601226 24047878 24051493 24067614 24610752 24613003 24069065 24044875 24044696 ...
#> $ compname : chr "Amador" "Amador" "Amador" "Amador" ...
#> $ comppct_r: int 45 10 3 3 10 10 85 5 3 3 ...
#> - attr(*, "SDA_id")= chr "Table"
## 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)
#> single result set, returning a data.frame
str(res)
#> 'data.frame': 609 obs. of 9 variables:
#> $ mukey : int 459154 459204 459205 459208 459208 459208 459208 459209 459209 459209 ...
#> $ cokey : int 24793311 24793145 24793604 24793157 24793158 24793159 24793156 24793317 24793320 24793318 ...
#> $ comppct_r : int 100 100 100 5 85 5 5 5 2 3 ...
#> $ compname : chr "Water" "Gravel pits" "Water" "Positas" ...
#> $ taxclname : chr NA NA NA NA ...
#> $ taxorder : chr NA NA NA NA ...
#> $ taxsuborder: chr NA NA NA NA ...
#> $ taxgrtgroup: chr NA NA NA NA ...
#> $ taxsubgrp : chr NA NA NA NA ...
#> - attr(*, "SDA_id")= chr "Table"
## 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
p <- wk::as_wkt(wk::rct(-120.9, 37.7, -120.8, 37.8))
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)
#> single result set, returning a data.frame
str(x)
#> 'data.frame': 337 obs. of 4 variables:
#> $ mukey : int 462527 462527 462527 462554 462554 462554 462555 462555 462555 462558 ...
#> $ cokey : int 24613423 24613424 24613425 24613451 24613452 24613453 24613021 24613022 24613023 24613673 ...
#> $ compname : chr "Alamo" "Madera" "San Joaquin" "Corning" ...
#> $ comppct_r: int 85 10 5 85 5 10 85 5 10 85 ...
#> - attr(*, "SDA_id")= chr "Table"
# }