Which map will the game use?

Forgive me if you read my last post with this problem, but I fear I so butchered the Topic Title and Description that no one who knows the answers is bothering to read it. Rather than self-bump it, I thought I should retry my tact.

I'm trying to figure out how the game decides:
a) whether or not to use a river map
b) when to use winter maps

So far I have found two variables (in the Early/High/Late.txt files) in which there is an option to say whether battles in that province will use a river map or not, one called "SetBorders::" and one called "SetAttributes::"

So far my fooling around has shown me that SetBorders may only define the text shown in the parchments when you right-click on a province and drag the cursor over a neighboring province. I have not fiddled with the SetAttributes variable yet because it doesn't seem to care from which neighboring province the attack was launched from, which mostly defeats the purpose here. Not every battle in Wessex should use a river map, only those with Mercia and (in my opinion/mod) Flanders.

I have not found any variable that has to do with winter maps yet.

I want to make all battles between Wessex and Flanders occur on a river map, how do I do that?

Also, say I wanted to make all battles in Sweden occur on winter maps, every time, how would I do that?