Do you have any idea of what the original map size was?
Not off the top of my head. Lemme see if I can check...
Looks to be 2600x2600 pixels.
Or how to screenshot the entire thing?
Well, if you really want to, the way is to get a really big monitor.
But that's not what I'm looking for. I'm honestly after the actual Age of Wonders map file, so that I can then take the screenshots and splice them together, and subsequently make any changes that we ever want to make to the map (and re-screenshot and splice).
I have AoW 1 on GOG.com and have the CDs for Shadow Magic.
While it might be cool to see what some of the existing maps would look like done in the AoW2 (3?) or Shadow Magic editors, that's much lower priority than getting them re-created in the original AoW editor.