Zoom out/in in Dwarf Fortress during gameplay

The mouse scroll-wheel works for me on Windows and Mac versions. The square bracket keys [ and ] also zoom out and in (respectively).

See: Dwarf fortress mode: Main Screen

Yes, it is. It is, I think, the only keyboard command not listed in green somewhere in the side menu, which is why so many people have trouble with it. To zoom in and out you hold shift and press either the > or < key (right next to the right-hand shift key) the number of zoom levels you wish to move, depending on which direction you wish to move, in oro out.