CUGIR files are compressed to reduce file size and download time. Packaging or "archiving" files together also makes them more portable. Many free utilities to extract compressed files are available online. Many are listed on Wikipedia's Comparison of file archivers. CUGIR does not support or recommend any particular software. When choosing a program, be sure to confirm it can handle the file types needing extraction (compressed or archived).
Types of File Compression
- .gz = Gzipped files. A compressed file format originally developed by Jean-Loup Gailly and Mark Adler and adopted by the Free Software Foundation's GNU project. Most file compression utilities can uncompress .gz files (including the free 7-Zip software), but it may be necessary to change the settings of the program to include support for .gz files by default. Look for options to change settings for file formats or file associations. A program called Gzip (Gnu Zip) that compresses and decompresses files, was also created by the authors. For more information on this format, see the gzip home page.
- .tar.gz = UNIX archived (using tar) and GZip compressed files. Files with .tar.gz extensions have been UNIX archived (using the tar command) and compressed (in Gzip format). An archive file contains multiple files when extracted. In the case of shapefiles, three or more files are tarred together and then gzipped to create a single compressed archive file.
- .zip = zip compressed files. Many newer data files in CUGIR are in standard .zip format, which any standard Windows, Unix, Linux, or Mac zip archive utility should be able to read and decompress.
- .Z = UNIX compressed files. Files with .Z extensions have been UNIX compressed. UNIX users can use the uncompress command to expand these files to their original form. Windows and Macintosh users can use the Gzip program, or other compatible decompression utilities.
Tips on Uncompressing Files
- If you have trouble extracting a file, try a different utility.
- If your file compression utility does not appear to recognize the compressed data package, you may need to change a setting (sometimes called "file associations") in the utility to recognize that file type (this is typically a problem for .tar and .gz data packages).
- ESRI software users should make sure the folders and directory names contain no spaces or special characters.
- Some files may extract to folders with the same name by default; you may need to extract data to uniquely named folders to avoid confusion.
- Some file formats require a conversion step before they can be used in GIS software; see the help topic on File Formats and GIS Software Compatibility for more information.
- See the help topic on CUGIR data packages for more information on the contents of downloaded data packages.