I don't know how accurate this is but I've been using it as a guide, apologies if anyone has posted it alreadyOK, so this is getting super-annoying... I heard reports this was fixed, but it doesn't seem to be? Just finished building this today:
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Have now built both types of Relay Station, only to get a Comms Installation at the end, and so still unable to build a Security Installation. Not really fun to just spam the same building which I don't want repeatedly while trying to "guess" what the right one is.
This is not exactly what I would call intuitive, in the same way as the sea is not above the sky. For example I built 3 Space Farms and would never have guessed they fed into the rather cryptically named Outpost Hub. Or know if it is bugged.
I also have a mining outpost that is 100% complete but still shows as being under construction, so I don't know if it is feeding into the Industrial Hub or not.