Supply line

In Fallout 4, supply lines can be created between settlements to share resources and inventory among them.

Requirements for creating supply lines:
 * At least 2 owned settlements
 * 1 free settler
 * At least Level 1 in the Local Leader perk

Benefits
Linking the settlements with supply lines provides the following benefits:
 * When building at a workshop or using a crafting station inside a linked settlement, one can use the junk inventory of all linked workshops from all linked settlements. (junk does not have to be salvaged first)
 * Armour, Weapons, Aid, and Miscellaneous items in your workshop are exclusive to the settlement. What is in your workshop inventory passes to that specific settlement's armor, weapon, chemistry, and cooking crafting stations.
 * Excess food and water will be used to supply all the settlements in the supply network. How a "green" shortage affects happiness in a settlement is not covered here.
 * In the PIP Boy "Workshop" menu, the game will show actual shortages for individual settlements with warning triangles, which causes unhappiness, but if the category is green, then the network is supplying the shortage.

Usage
To create a supply line, use the workshop in one of the settlements, highlight a settler and press [Q] (or RB/R1 on XBOX/PS4) to display a list of owned settlements. Select the settlement to which the player character wants to link the current settlement.

To review existing supply lines, open the world map and press [C] (or L1/LB on PS4/XBOX) to view all the settlements connected to the Supply Line network.

Settlers assigned to supply lines will become Provisioners and will travel between settlements (usually leading a pack-brahmin). To remove the supply line, simply reassign the Provisioner to some other work object in their settlement.


 * The Provisioner will actually travel between the two connected settlements, so it may be difficult to reassign the worker, since they may not be in their home settlement.
 * Provisoners still count towards the population limit of their respective settlements, as well as food/water requirements, despite hardly ever being in the settlement.
 * Settlements share resources with all other settlements that are part of its supply line network. Two settlements do not have to be directly connected. In other words, if the Sole Survivor connects settlement A → B, B → C, and C → D, then A, C, and D will also share resources with each other despite not directly being connected since they are still part of the same network.
 * Provisioners will engage hostile creatures and enemies along their path, so it is advisable to equip them with appropriate weapons and armor so they can defend themselves.
 * Like companions, provisioners cannot die by enemy fire; with enough damage, provisioners will be briefly knocked down, but they will get back up after a while. They will, however, die from damage taken from Sole Survivor's mines.
 * To change or update the Provisioner's clothing or weapons initiate dialogue and trade items with them.
 * Creating a supply network with two overlapping circles (A → B → C → D → A and A → C) can make some of the settlements have their food/water set to 0. To fix this one needs to remove one of the circles and then activate the workshop at the affected settlements to update their resources.

Bugs

 * When setting up a supply line, only settlements which are at least one settler under the population limit can be selected as target. This may be a possible bug, since provisioners do not change the population of the targeted settlement.
 * It is still possible that provisioners will occasionally disappear, requiring a re-establishment of a supply line. This may be a possible bug, and not the provisioner dying while traveling.
 * When assigning a settler to form a supply line between two settlements giving them the title of "Provisioner", and then moving that provisioner to the settlement they will be doing a supply line to, the settler will travel there, but remain with the provisioner title and backpack appearance. No brahmin, however, will spawn as the settler stays there. Despite, the title and appearance though, the provisioner can do everything a settler can do, including be assigned to certain tasks.
 * Supply caravans and their respective provisioners can become stuck on their routes or just disappear despite the Pip-Boy still showing a supply line connected between two settlements. This can make it extremely difficult or impossible to make any changes to your supply lines after they have been established.
 * When reassigning a provisioner from one supply route to another, to a new settler task, or making them move to a new settlement, the old supply route will remain active in the pipboy supply lines map, and the resources from the previous route will still be available to the provisioners original settlement.