Mini-freighters ( a miniature version of the freighters move on the map ). On your trade screen they come out as blue triangles, and they also show you the direction they are moving. Try to generate the parallelogram trade route with your imagination. Best I can do.
My previous statement was from experiences. I have only paid attention so many times, and that's what seems to be the rule so far. Worked for all trade routes that have been primarily vertical and once for a primarily horizontal trade route (that I have seen of course).
Meant to add something in my last post, too. There are advanced trade maximizing tactics that demand all your trade enhancing starbases be in the same sector. They can be found in the unofficial strat guide. Even if you do not use these advance tactics, it may be in your best interest to build all your trade-enhancers in the same sector.
50% of 50 for 12 out of 70 turns is far better than 50% of 50 for 7 turns is far better than 50% of 34 for 7 turns. You get the idea.
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