Campaign Map "Zoom"?

[Myrddraal]

You can also use your mouse wheel to zoom in on the map.

Exactly. It depends what you mean. The mouse wheel will zoom you in and out, but if you want more tiles per area you'd have to rework the map. (There's a tutorial (by Monkwarrior I think) which explains step by step how to make a new campaign map from a zoomed in region of the vanilla)