Edit: Updated math because I shouldn't make topics like this immediately before going to bed.
The old map (that we could see) was 256x256 tiles for a total of 65,536 tiles.
I've observed that the map has been expanded 100 tiles in one direction, and so assuming the map is still square, that means the new map is 456x456 tiles for a total of 207,936 tiles.
So as you can see, the map is now over three times bigger than before.