SDA_query: Query Soil Data Access

Description

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.

Usage

SDA_query(q)

Value

a data.frame result (NULL if empty, try-error on error)

Arguments

q: A valid T-SQL query surrounded by double quotes

Author

D.E. Beaudette

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

Run this code

# \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)
  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 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
  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)
   str(x)
# }

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