[tinkthank]

I am trying to fix up the Ormus map (there are a few neighbors issues), when I also noticed a small terrain issue. So I wanted to go in and fix it up, and see that some terrains have really odd numbers, and have now seen this on other maps too. I don't get it, can someone help me?
For example:

#terrain 25 1537

What the heck? According to the mapedit.pdf, the valid terrain commands are:

1=small, 2=large, 4=sea, 8=rivers, 16=mountain,
32=swamp, 64=waste, 128=forest and 256=farm.

This province happens to be Plains. I could understand a 1, or a 2, or a 9 or a 10 if need be, but what does this number mean? And why?
In fact, I notice that a whole lot of terrain numbers on lots of nice maps have numbers which I dont get at all. Is there a list somewhere I am missing?
Thanks so very much.