Why did they use vertical trade lanes?

[Australopithecus]

I imagine that vertical manouvering would be easier to do and would allow certain sections of the traffic to have an ''incoming'' height and an ''outgoing'' height for all ships to remain in.

In this situation, traffic will sag a bit, that's all, no biggy.
like - external site : marinetraffic - Reds are tankers, Greens are cargo vessels.
It wont be a straight line from A to B, not quite.
Assuming there's like an imaginary RP where houses carry goods all the time and don't bother players with npcs.

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