The third Fallout 4 DLC, Far Harbor was released yesterday and as promised it offers a massive new landmass. A visual comparison between the sizes of the Commonwealth and Far Harbor‘s map has been done by Gamepedia which gives us a clear idea about new DLC’s map.
Bethesda had already confirmed during the reveal that Far Harbor would be the biggest DLC that the team had worked on in term of landmass. The size of Far Harbor is even bigger than The Elder Scrolls IV: Oblivion‘s DLC Shivering Isles, which is massive.
Here is the image which will give you an idea of the Far Harbor‘s map:
And here is the Fallout 4‘s basic world map:
By scaling the maps we can come to a conclusion that the size of Far Harbor‘s map is around 20% that of the Commonwealth’s. You can scale the map of Far Harbor by corresponding one cell to each square on the grid. On the other hand, each square in the Commonwealth map corresponds to four cells (2×2).