Tarred & Zipped Files (.tar.gz)

The .tar file format (derived from Tape ARchive) is a type of archive file traditionally produced by Unix almost specifically for backup purposes.

The GNU Zip program (also Unix based) is used to compress files much like WinZip would in our Microsoft world – but if several files need to be compressed together, they must be tarred together first (thus the extension .tar.gz).

So in a nutshell, if you run across GIS data that carries the extension “.tar.gz,” (as is the case if you download from the National Atlas) you’re looking at a UNIX formatted zip file that can be opened with most unzipping programs – but NOT with out-of-the-box Windows.

Example: If you’ve taken a GIS class with me, you know I like to start with a discussion of coordinate zones and then move directly to an import of the US County Boundaries (countyp020.tar.gz). But you can’t open the file with Windows, so I’ve installed WinZip. Double click on the tarred and zipped file, and you’ll get the following message:

Simply select the “Yes” button, and unzip the file(s) as usual.

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