There was a tute I read a while back by a Vue great...consarn it but I can't remember his name, on using B&W images to control ecosystem placement, one would imagine you could use greyscale maps the same way for control of densities....haven't tried it ...box too slow and low RAM, but it shoulsd work. Look up the tute, should be in the Backroom if anywhere...

 

Once in a while I look around,
I see a sound
and try to write it down
Sometimes they come out very soft
Tinkling light sound
The Sun comes up again