Google Earth uses streaming imagery over the Internet to provide you with incredible images of our world. But what if you don't have an Internet connection available at any given time?
If an Internet connection becomes unavailable, Google Earth shows you whatever imagery is in its cache. While online, however, you can effectively save imagery on your computer for offline viewing later. This works best when you increase the cache size and then browse a particular geographic area before you take the computer offline.
For example, when I was in Moab, UT last fall, I wanted to be able to show some terrain around Moab to others without an Internet connection. To do this, I first followed the aforementioned steps. To make sure that the cache included the specific imagery I wanted to display, I set up a set of placemarks of the Moab terrain, placed them in a folder and played a perpetual tour of the folder while the computer was still online. This saved the imagery in the cache.
When I arrived in Moab with no Internet connection, I was able to show high quality imagery in Google Earth.