I think that's what borders are for. A border around a zone does not have to be a literal border, a wall or a fence, but it represents the difficulty to move into another zone. This might be different for different skills. Walking over a parking lot with leaves scattered around might not impair your movement all that much, but it will definitely raise the difficulty of doing it quietly. Rocky Terrain, rain-slick asphalt, broken glass, can easily increase the borders of a zone for movement. Darkness, fog, bright sunlight could be borders for someone trying to shoot, although that should probably be done by declarations on the side of the defence roll.
The problem with zones in general is, that they are always of a somewhat arbitrary size, they will never be exact. But they don't need to be, they are only there to create a rough outline of the area the conflict takes place. A usual living space would probably have each room as a different zone (the small bathroom as well as the large living room). An opera hall would have to be cut into smaller pieces (stage, each aisle, different rows of chairs [which would have a rather high border, crossing those rows is not too easy]).
If the terrain is too big to be reasonably represented by zones (an open field could be laid out by let's say 10x10 or more identical zones, but that would be just insane), just don't. Instead, go for a cat and mouse game or something similar, so one character can force the other into an "arena", an area to fight in that can be represented by zones (from the field to the barn, where you are standing with your back to the wall or run inside). If the "prey" gets away, there will not be a conflict this time, if the hunter can chase him to the right place, it is on. If none of the characters are running, you only have 1 zone, the one they are in, and that will be all there is to it in that fight, unless someone changes the pace of the conflict.
I hope I'm not just mumbling nonsense right now, I will check again later.
And I am not sure though, what exactly you mean by battlemaps.