ezpz
what does a cartographer have to do with this? i think you're kinda missing the point. a cartographer only records what is already there; the map showing a spiral pattern made up of cloud-like matter in hyperspace is because
there is an actual spiral pattern made up of actual cloud-like matter in actual hyperspace. and i'm pretty sure it wasn't put there by some human cartographer who just really liked drawing spiral patterns of celestial clouds.
what we've been speculating about is why star systems that have been labeled and used by humans as 'core systems' just so happen to be at the center of a rather remarkable celestial formation. human core worlds being at the center of such a thing is a bit like earth being the center of the universe, obviously, because it is clearly where all the important stuff happens. except... it really does not work that way in reality.
i think there are pretty much four possible explanations for this:
1) the zone that was colonized by humans is right at the center of this massive hyperterrain pattern by pure coincidence. would be a pretty crazy coincidence, though.
2) the Domain was aware of the spiral, and deliberately chose its center as target of their initial colonization efforts.
3) the pattern didn't exist before humans (or human-made machines) arrived in the Sector, and was somehow shaped by human activity.
4) sort of a combination of 2) and 3), the pattern was created deliberately and actively by the Domain or the Sector's current inhabitants.
leaving aside 1), mostly because it would just be boring, it's interesting to speculate about the why and how of these explanations. maybe settling at the spiral's center offers some kind of advantage. or maybe it is merely a curious side effect of the old gate network, or of countless fleets transitioning to and from hyperspace around the core worlds -- kinda like waves on a water surface, forming when something enters or leaves the water with some force.