From GPSur Dr. Erhard Regener:
May I use "Google Earth" even without internet? Yes: Without Internet "Google Earth" cannot load new maps, but the former visited maps stay in the computer. "Google Earth" remembers images and maps once shown in the screen in its so called Cache memory. This cache is stored to the local disk and therefore also available without internet connection. Therefore it is also called offline memory. As long as this cache isn't full all recently "overflowed" areas are still available. And exactly this is the problem! When the cache is full it overwrites the oldest data by newer ones. Nobody knows when the cache is full and less which data are automatically overwritten. If I need a specific area after weeks for a presentation without internet these data are lost. There's only a fuzzy background without details. "Google Earth" has overwritten exactly this area because someone has prepared his holiday trip on the same computer. All the worse if you wanted to use "Google Earth" with GPS out of home and the necessary maps have disappeared. Google Earth itself provides no opportunity to backup its cache data or to transfer it to another computer. At this point apply "Cache for Google Earth". Backup your cache with precisely that maps you need for later use. Stay informed about the "filling level" of the cache. Exchange prepared cache copies with other computers.