Not really sure, as we don't know the map scale. But it is large enough to field armies numbering in the tens of thousands without leaving home anywhere close to undefended.

So its not unlikely that it covers much of that sector. There might be a few places not yet conquered, but we'd guess most of the North-eastern sector of the continent belongs to the Empire. We didn't define it all as we're open for others to define parts too. But it would make sense that they've conquered all the easy parts before they go for the harder parts. Of course, tunneling beneath the mountains (through use of captive Evokers) will be most unexpected. And it'd provide a natural road for Imperial expansion.

We don't want to decide everything for the Empire ourselves.

EDIT: We don't know how it'll work out either. That's the fun bit.