An official website of the United States government
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Official websites use .gov A .gov website belongs to an official government organization in the United States.
Secure .gov websites use HTTPS A lock ( Lock A locked padlock ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.
Detailed current and historical definitions, delineation information, lists and data files, and links to other products related to selected types of geography.
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