get_nhd
returns a list of `sf` objects extracted
from the National Hydrography Dataset.
Arguments
- template
A `Raster*`, `Spatial*`, or `sf` object to serve as a template for cropping.
- label
A character string naming the study area.
- nhdplus
Extract data from the USGS NHDPlus High Resolution service (experimental)
- extraction.dir
A character string indicating where the extracted and cropped NHD data should be put.
- force.redo
If an extraction for this template and label already exists, should a new one be created?