Grid2Polygons has been placed under a GNU General Public License (version >= 2).
I believe this to be as close as possible to public domain while satisfying the 
license requirements of dependencies (including system dependencies) of this 
package. Note that all source, data files and other contents of the 
Grid2Polygons package are in the public domain because these materials 
originally came from the United States Geological Survey (USGS), an agency of 
the United States Department of Interior. For more information, see the official
USGS copyright policy at
http://www.usgs.gov/visual-id/credit_usgs.html#copyright