Thanks Kate, I see what you are saying but I thought using collections was the way to handle this? The 800 maps are all organised in collections of about 40 maps each. Each map is only 10-30 MB (optimized PDF’s), so when a collection is open only one actual map is open from each collection at a time. The users switch between the collections which each have a theme (ie imagery, topo, geology etc). So overall the performance time/speed/functionality seems to be pretty good. The main problem was the memory usage of the SD card (filling it up). The 2:1 ratio now makes sense (tiling) so I just need to allow 3 x the map folder size for the overall storage overhead. If I can sort out the partitioning then I think I have a winning solution to my storage problem.
Due to the cost of the larger SD cards, it would be neat to be able to use a smaller (64 GB) card for each project and be able to simply insert the right card for the job, without having to *sigh* load all the maps again by hand each time. The way I see it, I should be able to pop in the right card, open Avenza and have all the collections for that card right there and ready to go.