DOI and USGS link policies apply | U.S. Geological Survey Official websites use .gov .gov website belongs to an official government organization in the United States. Secure .gov websites use HTTPS lock ( or means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites. DOI and USGS link policies apply Link policies and requirements When links to third-party sites, or embedded content from third-party sites, are used then the DOI and USGS link policies apply. Was this page helpful?