The entire Google Earth database is huge; installing it on a normal PC is impossible. So Google Earth downloads small parts of the database, as they are needed by you. Hence Google Earth requires internet access to download the visual map data that you need to view. The data is then stored in a cache directory where it remains, even after a reboot. So if we load our cache up first, we are still able to use Google Earth, even if we are working somewhere that has no internet access.
The traditional method of ‘loading the cache’ involves:
(1) Start Google Earth Application
(2) Zoom in to the area you are interested in, at the zoom level you require.
(3) ‘Pan’ around the area. As you travel around, the cache will be loaded.
The drawbacks of using this method are that it is very time intensive and you may miss some of the area.
There is an alternative method of cache loading, using the relatively new Google Earth ‘Tour’ feature. By ‘Touring’ along a path, we can load the cache automatically. Large areas can be covered using a path – then simply run the tour and do something else while the cache loads.
A path can be created manually in Google Earth – select Add/Path, then draw a nice ‘snake game’ style path across the area you want to cache.
I have also included an excel spreadsheet that will create a Google Earth path (.kml format) that you can use to scan a rectangular area. See the Automated cache loading page for details.
Before we continue, with this loading the cache demo, you need to make a path on Google Earth. Create one manually or use the spreadsheet, it is up to you.
With Google Earth open, you should find your path located somewhere under My Places.
Now, make sure that the ‘Tour’ options are correct.
Select Tools/Options/Touring, there are 3 values we must check:
(1) Camera tilt angle – Set to 0 degrees, as we wish to view the map from directly above.
(2) Camera range – This controls the level of zoom, a lower value will zoom closer to the ground and will load much more data into the cache. As a quick guide, you might want to choose 1000m if you want to scan a city area (you will be able to see individual buildings clearly). Or you could choose 5000m if you wanted to cache a larger area e.g. an entire province, without overfilling your cache. I found that the 1000m setting provided a clear image down to 150-200m, whilst 5000m was still clear at 1000m. These findings can vary depending on the area you are scanning though (Google Earth photographic details vary, depending on the country and region that you are looking at). You only need to worry about how low you need to zoom, the imagery for your area at greater camera heights will automatically be cached when you run the tour (e.g. running a tour at 1000m will allow you to view imagery at 2500m and 5000m).
(3) Speed – How fast the tour will run. You may be in a hurry and need to load your cache quickly; setting your speed to a higher value will help in this situation, but don’t set it too high for your computer processor and internet connection. Touring too fast will cause the cache not to load successfully. In testing with a normal windows laptop and an 8MB download internet connection, you can download at a speed of 200 with a camera range of 1000m or 800 with a camera range of 5000m.
Always check the zoom before you ‘Tour’. If you have the wrong setting you will have wasted a load of your time. Apply any changes, so that the settings are saved.
Select your path; in the bottom right corner of the Places menu you will see the ‘Tour’ button 
. Press the button and away you go! The cache will be loaded.
In order to make sure your data remains in the cache, I have noted that you should exit Google Earth after loading a cache and then open it again with an internet connection still present. This seems to validate the cache in some way. If you don’t follow this step and immediately try to start using Google Earth offline, you might find that your cache is deleted.
You may be wondering how close to make your path lines, so that you are not overlapping too much or missing data. It’s complicated, so I have included more details under the Automated cache loading page. The spreadsheet makes it much easier to correctly space your path lines and removes the chance of missing data. It also calculates the tour time and makes estimates of the cache size used by each path.You may want to do some testing of your own computer system to make sure you can get the best settings. Consider the following:
(1) Your Internet speed
(2) Your computer speed – Computer processor & RAM
(3) Windows Display settings – more pixels = more data to download
(4) Google Earth Display Settings – (Tools->Options->3D View) again more pixels to download
(5) Camera range – Not only will a lower zoom range require a slower tour speed, the additional data may also fill up your cache and overwrite older data.
One final thing to consider is the location you want to cache: cities such as London or Paris have much more data per square kilometer than a rural area, perhaps 10 times as much! The layers that you select (e.g. 3D buildings) will also add to data consumption.
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