M2TW and ETW use your position on the map for the battle map.

I am not convinced that NTW does that. I think to some extent it may in some regions but I have found my self fighting on the same map more than once.

Sieges or city battles are all on flat maps for the greatest part. There are different maps for the side of the city you are fighting for but most are not too varied.

Ambushes are all quite similar too. There only seem to be a few variants of the map.

The regional battle maps are a little better but they seem to have some kind of priority.
The first map you will usually fight on is a flat one and if you have a second battle in the same region it may have some hills.