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 settlement, one can use the inventory of all linked workshops/crafting stations (though the shared items will not all show up in the workspace, they will automatically be used when crafting/building).
 * Even non-junk items will be shared, so long as they are in the workspace (such as mods or items like Purified Water); they will automatically be used when a recipe calls for it.
 * Even Bottlecaps will be shared, so long as they are in a workspace (common if having many different settlements with stores). This is most noticeable if trying to build a new store (which requires some number of caps); the caps in settlement mode may be much higher than the caps in the inventory; it is possible to build stores exclusively from caps stored in workspaces throughout all the settlements.
 * Excess food/water will be used to supply the settlements in the supply network with shortages; this is only indicated by the normal "red" display for food/water shortages being green. Moreover, it may not turn green immediately; doing something to force the UI to update, such as assigning another settler to a defense job may correct this.
 * In the PIP Boy "Workshop" menu, the game may still show a food/water shortage in settlements that have less food or water than their population, but so long as having supply lines established, all that matters is the total population compared to the total food and water production the Sole Survivor has within the connected supply network.

Usage
To create a supply line, use the workshop in one of the settlements, highlight a settler and press [Q] (or R1/RB on PS4/XBOX) to display a list of owned settlements. Select the settlement to which the player character want 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). If wanting to remove the supply line, simply reassign the Provisioner to some other work object in their settlement.

To change or update the Provisioners clothing or weapons initiate dialogue and trade items with them.
 * 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 Surivor connects settlement A → B, B → C, and B → 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.
 * Provisioners cannot die by enemy fire, but can die by player character placed mines. Like companions, when taken enough damage, provisioners will be briefly knocked down, but they will get back up after a while.
 * 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.
 * 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.