a) civilized areas (various different songs playing in different areas)
B) wilderness
c) dungeon
d) night (?)
In Morrowind:
a) combat
B) everywhere else
In Oblivion:
a) combat
B) towns
c) wilderness
d) dungeons
Essentially, my suggestion is that a new category is added on top of Oblivions, Escape/Chase.
Whenever the following situations are fulfilled, chase/escape music plays:
a) an NPC flees from you
B) you've been caught trespassing by a guard AND
c) you are actively running away from a guard with your weapon sheathed