Timothy Lochner one of the game and tools programmers from Daybreak just replied to a post on Reddit and gave away some size details of the upcoming new map.
The new map will be slightly larger than the old one. A lot of valuable play space is wasted in the mountains around the border, so we are expanding the map by 1km in each direction. So instead of an 8x8 map with ~6x6 play space, it will instead be 10x10 with roughly 8x8 play space.
Source: Reddit