@Jester: I just ran the math on your huge maps:

4096x4096 with 16x16 tiles at 32 bits per pixel = 4096*4096*16*16*4 = 17,179,869,184 bytes, or 16GB(!) per image!  And that's just for one layer!  You said you were doing 8, which brings it to a whopping 128GB   No idea how that ever worked...

Hmm, maybe I remember wrong. Most of my maps were for randomly generated environments, so I usually didn't have to actually fill them out by hand.

Not all maps had so many layers though (usually less, the Majestic made most normal uses of layering kind of silly), and not all maps were so large.

I usually only did stuff like that for demos of terrain generation, or for SimCity style, modifiable maps. Which tended to have fewer layers.