Arguments
template
A Raster* or Spatial* object to serve
as a template for cropping.
label
A character string naming the study area.
res
A character string defining the resolution of the NHD to download.
Either "medium" (the default), or "high".
raw.dir
A character string indicating where raw downloaded files should be put.
The directory will be created if missing. Defaults to "./RAW/NHD/".
extraction.dir
A character string indicating where the extracted and cropped NHD shapefiles should be put.
The directory will be created if missing. Defaults to "./EXTRACTIONS/NHD/".
force.redo
If an extraction for this template and label already exists, should a new one be created?