[MiWa]

Memory is mostly consumed by the 'chopped' map_c.tga. I think this file is by far the largest.
If you have all sea and a couple of islands you can have a huge map because it is mostly sea and map_c.tga
is compressed significantly. It is the shores and rivers that make compressed map_c.tga big.
In other words, blocks which contain both water and land can't be compressed.
So I doubt that actual dimensions of the map are the key, it is the byte size of the compressed
map_c.tga which causes problems.