After asking the question I looked at the Arduplane wiki and found the following...
Tips
Prefetch: You can cache map data so you don't need Internet access at the field. Click the Prefetch button, and hold down Alt to draw a box to download the selected imagery of a location.
So I figure I found the answer my self but if anyone has any comments to add, it would be much appreciated.
Replies
After asking the question I looked at the Arduplane wiki and found the following...
Tips
Prefetch: You can cache map data so you don't need Internet access at the field. Click the Prefetch button, and hold down Alt to draw a box to download the selected imagery of a location.
So I figure I found the answer my self but if anyone has any comments to add, it would be much appreciated.