As a TT veteran, I have the habit of making a network of ressources and goods. While playing, the game informations are very obscure to know if it's possible.

Practical example from my freeplay:

I have a petrol field on the left, a petrol field in the center and a refinery on the right. Thus before I get to faster means of transportation, I would like to make a line between left and center to gather all the petrol at the center station so the second transport can always be full when it goes to the refinery.

The main problem in the game is that you can't give direct orders to a transport to unload its shipment at a specific station as while configuring the line, it only mentions the loading.

So if any dev drops by, can it be possible to better this system instead of having to guess how the transport will behave when "left on its own"?

From the official site's FAQ, it seems cargo can switch transportation mode / route to their final destination.

Q: Do passengers and cargo change modes of transportation during a journey?
A: Passengers and cargo will change several times to reach their destination, as long as the total travel time or costs stay within a certain range.

The reason there isn't any instruction for unloading is that cargo in TF is entirely demand based, nothing will ever be produced if it doesn't already have a destination.

The problem with the situation that you're describing is that it's highly unlikely that the petrol field on the left will ever be used because the the AI isn't going to pay for shipping something all the way across the map when there is already a much closer field that is already producing.

mmmm, that sounds like a stupid AI as IRL it would still pay off. I'll try to check that in my next gameplay session...

Actually, disregard what I said. I spent some time running tests and now I'm not at all sure how the game is making it's cargo decisions. In Train Fever it was based on distance and time but in Transport Fever neither of those seem to be deciding factors. In Train Fever the closest supply would have always been used but now in Transport Fever when you attach more than one supply to a manufacturing facility the production at the suppy sources fluctuates in strange ways.

I too am struggling to figure out how the production works. I have trains queuing up, lots of raw material stored but the factory isnt producing...

I dont understand how to estimate the production to optimise my routes.

A company will only have so much finished good not moving to its costumer before it shuts production.
You shoul always prioritice as far downstream as possible. Contrary to TT this game favors pull logistics rather than push.