Why can't I open a Google Earth map file
When you download a map file, it should be automatically opened by Google Earth. However, if your computer has not been set up correctly, you will receive a message that the file type is not recognised, asking you to specify which program should be used to open the file.
The exact procedure for specifying Google Earth as the program to use depends on your computer system software and browser software.Typically you are given a list of programs to pick from and / or the option to browse for the program. You should also tick any check box that says always use this program for this type of file so that you only need to do this set up procedure once.
Google Earth uses 2 types of map file - kml, which is the standard file type and kmz which is a compressed (zipped) version of the standard file type. kmz files are much smaller in size and are recomended for large kml files. We have recently changed from using kml files to kmz files, achieving an average of 14:1 reduction in file size and considerably shorter download times as a result.