[asheshouse]

No one has mentioned ed_map_t.tga yet.

This is another way to define water land boundaries.

I've used it on Battle of France to prevent vehicles crossing rivers.
It also improved the extent of navigable areas around the coast.

Although rivers are indicated sufficiently to prevent vehicle movement I presume they are not wide enough to allow river traffic. If I made them wider then land traffic was unable to access large trips of land on the river banks.

So various factors at work:

map_T --- RGB 28
ed-map_t.tga
map_c ?

Bit of experimentation required maybe.