"For owners of both WARHAMMER I and WARHAMMER II, our first content release shortly after launch (free of course) will be a vast, combined campaign map representing the geographical areas of both games in a single map" - so by this im getting that its not the actual maps stitched together but more a smaller map representing them.
I'v come to the conclusion from some of the things the devs have said in interview , The mega map is both warhammer 1 and 2 maps put together but after reading comments from the devs im worried it wont be the actual two maps stitched together but more a smaller map repersenting them.