An official website of the United States government
Here’s how you know
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.
These compressed files are large. Select a layer below or connect directly to our ftp site to download the files. We strongly suggest you access these files through our site using an ftp client (anonymous log-in and password).
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