To my understanding, the maps are bigger. When they tested Archipelago, they ran into problems with the small islands and the district system. In order for the inclusion of the archipelago map type with bigger islands that don't cripple the district system, they would need larger map sizes. I think overall, they would need larger map sizes anyway. To the point, from what I've heard from the videos and previews, the maps are bigger. It wouldn't make sense to mention it if it was just that the land area was spread out and there was less water.