Fetch map unit geometry from the SDA website by WGS84 bounding box. There is a limit on the amount of data returned as serialized JSON (~32Mb) and a total record limit of 100,000.
mapunit_geom_by_ll_bbox(bbox, source = "sda")a bounding box in WGS coordinates
the source database, currently limited to soil data access (SDA)
A SpatialPolygonsDataFrame of map unit polygons, in WGS84 (long,lat) coordinates.
The SDA website can be found at https://sdmdataaccess.nrcs.usda.gov. See examples for bounding box formatting.