The world in the isometric projection is indeed diamond-shaped. North must coincide with either the top-right side of the diamond or the top-left side of the diamond. At the moment, the game is giving somewhat controversial directions in this regard:
for example, the North Ward in the Brackenbury Sanitarium is located in the top-right corner of the map. The dragon in the "Parable of Wael" quest is facing in the same direction, and it's described as east there.
Eastern Barbican in the stronghold faces bottom-right, but Western Barbican faces bottom-left, which should be south if we go by the neighbouring barbican.
Hope this clears the question up.