Fallout 4: set up supply-lines for easier settlement management
I keep learning things as I go along in this game, which is excellent although it is inundated with bugs along the way.
One of the things that you don't actually have to do in order to finish the game but to me is a lot of fun is setting up settlements and maintaining them to have a bunch of people on your side as well as places to go and rest and restock on supplies.
But this can be kind of annoying until you figure out about trade lines because each settlement keeps its own supplies, and unless you want to run back and forth with supplies between each one, they do not share.
The system doesn't do a very good job of explaining this to you. In fact, it doesn't, as far as I have seen, let you know about it at all.

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I recall that I was getting annoyed because I had been salvaging all sorts of things that will give you cloth in your inventory but I kept returning to one of my settlements and they were always complaining about not having enough beds. I would try to make them beds only to discover that there wasn't enough cloth to do so. But I had just returned from a rather long mission, scrapped a bunch of stuff that contained cloth, yet it is telling me that I don't have any. Well, therein lies the problem: Each settlement has their own storage or cache of materials.
I figured that since I am the leader of all of this, that the stash was MINE, not that of the settlements. WRONG!
In order to set up supply/trade lines you have to unlock a perk in your leveling up that previously might not have seemed at all important and maybe you didn't even know what to make of it.

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Tis called "Local Leader" and it is a perk located below charisma. Fortunately for me I had already invested in Charisma because I enjoy being able to manipulate people in conversation - it is a very fun part of the whole experience to me - but if you didn't you will need to have I think 5 or 6 charisma before you can unlock this perk. Once you do, you can establish supply lines between settlements, but it's not so simple as just unlocking the perk, you have to assign someone to actually do the route.

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Find a lazy unassigned settler and then look on the bottom of the screen for the option that says something about "supply line". Once you assign this, this settler will endlessly walk back and forth from the two areas and this now means they will share the same resources and you can build to your heart's content.
For me, I built a ton of sleeping bags at the Starlight Drive-in becuase they had been pestering me for a while about the lack of sleeping arrangements. Another benefit of these supply lines and you may have noticed it while looking at your own settlements, that some of these places have HUGE farms but very few people. Well now that huge amount of food will be shared among all the connected areas you established. No need to build enormous farms at all of them. The same goes for water. You can just have one huge water farm somewhere and then it will be shared across all settlements.
This should save you a bunch of time and eliminate a bunch of frustration. Getting the perk initially might seem like a pain but it is totally worth it if you are interested in having supplies at all of your settlements to facilitate easier building at all of them.

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NOTE: IT is not necessary to connect every single settlement with every other settlement. Just like the above picture suggests, if you set up a "hub" settlement it will supply all of them even from other sources. Each settlement just needs to be connected in some way to the others. The only way they will end up not sharing is if their is a break in your supply line somewhere and a place or places end up isolated.
Once I did this I started to set up recruitment beacons and my population just exploded. This will encourage invasions at your settlements but if you set up just a small level of defense, they can handle all the assaults that I have seen so far. It's kind of fun to witness them actually and you can even take part if you want to.