Originally Posted by jimjam
I will try to aswer some of your questions. If you don┤t understand my aswer, or if I don┤t aswer you accordinlly, feel free to ask again.
Most of the files stored in the database are .KMZ (stands for KML Zip), that is a compressed format of .KML, for two reasons: Use of less space, and the possibillity of packing multiple files.
The .KML file itself are just instructions for the GE program to execute, like, placing specific landmarks, paths and so. No image information is inside a .KML file, just Lat/Lon instructions for GE to get information from GE server. (this is a bit less than real, this is just an intro to .kml). The structure of a .kml file is human-readable, just like an HTML pages, with tags and such.
However, there is a function of GE called Image Overlays, that allows you to put a image onto the globe, for your own purposes. (Like a more detailed map, demographic info, etc). And now, the multiple packing property of .KMZ files is useful, because one can use it to distribute many image overlays within a single file. If you use .KML to do this, you will need to hand over also the images of the overlay, or host them in a site, for the user that opens that .KML fetches it from the site.