Compressed Data

There are two types of compression:

• Lossless.  If you cannot tolerate changes in the data, it must be lossless.  Some kinds of files, like text, can still get very good compression.  Examples include the DOCX and PPTX formats for Microsoft Office, or the LAZ format for Lidar point clouds which reduces file sizes to 10-20% of the original.
• Lossy.  If you are willing to trade some data quality for additional compression, lossy compression works.  Examples include DVDs, MP3 and other music formats, and JPEG photos.  Mapping examples include MrSid or JPEG2000.

Compression of GIS data often uses standard Windows ZIP compression, but often uses Unix TAR and GZIP.

Last revision 3/27/2014