"Is north that way?"
I can't quite get my head around how speaker proximity works with direction. Like, if I'm standing due west of you, and you're due east of me, then would west be kochira, east sochira, and north and south would be achira? Or are all cardinal directions achira, since their terminal points are far from everyone?
I suppose if you were talking to Santa Claus, north would be sochira.
This is just me, but the internal context of the sentence would indicate acchi.
Normally, we use acchi/socchi when defining the spatial relationship between two people and an object. North,however, is not an object. It is a direction vector. The starting point is were we are, but there is no end point. Northness goes on forever. So, to me, acchi makes the most sense.