Thanks for the information. I've seen the articles/illustrated examples on soasewiki.com, and while they do provide a great breadth of information on the trading system, they still leave me with one question: what conditions govern the behavior of the trade line? Essentially, how does it decide to connect to the next trade port, and how does it decide on a path?
I have observed that the line does not always continue on to the next trade port, even in my most simple tests. When attempting to construct a more or less linear trade line through adjacent planets, I reached a point where the line did not continue on to the next trade point in the line. It didn't even require a jump through a UCGW. (In this line I had one UCGW jump earlier in the line, but all other segments were between adjacent planets.) I haven't been able to figure out what conditions would make the line continue through the other trade ports, but stop expanding at a certain one though I continued with an identical pattern of construction.
Also, in this particular test, I think the planet at which it stopped only had two phase lanes, one into it along the path of the trade lane, and one out of it to the next planet where I placed a trade port. This makes me curious about what happens when more complexity is introduced. What if a planet has several phase lanes and you place trade ports at more than one adjacent planet (other than the previous trade port leading "into" the planet)? A fork in the road. How is it determined which path the trade line will take? Or does the line simply end when it has more than one place to go?
As far as the build order of the trade ports, I think (I'll have to confirm this) when I scuttled the first trade port, the starting point of the trade line moved to the second trade port I built, and so on. This may be coincidence, due to the linear nature of a large part of my tests, but I still think the trade line originates at the oldest trade port.
I haven't been able to draw many conclusions from my observations. The line seems to behave almost counter-intuitively. But I think that this information could be useful, especially in large maps where this kind of planning is needed to ensure economic efficiency.