A .zip file is a compressed file or group of files. To use these files on a GPS unit they must first be extracted into a separate folder. The extracted files may then be copied to the GPS unit.
Extracting .zip files varies on different platforms (ex. different versions of Windows OS, Macs, etc.). On newer versions of some operating systems extracting these files is as simple as right clicking on the .zip file and selecting ‘Extract’ or ‘Extract All…’. If this option is not available to you, you’ll need to do some research on your operating system to find out how to extract the files.
Commonly used extraction applications on older Windows operating systems include the free gzip application (http://www.gzip.org/) and the paid WinZip product.