There are lots of areas in the UI where the mouse wheel scrolls the display up and down: The Chat window, the Character sheet, the list of Stats and Actions, the layers on the map editor… It happens a lot and it’s really intuitive. While in this mode, shift-wheel scrolls horizontally, which is also really intuitive.
But if the mouse is accidentally over the map when I scroll, the map zooms in and out and it often throws me off.
I’d prefer option-wheel to zoom on the map, and wheel/shift-wheel to scroll the map (I prefer horizontal/vertical scrolling over option-dragging). But even if you don’t implement horizontal and vertical scrolling for maps, making option-wheel required to scroll would reduce accidental zooming.