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 your settlements with supply lines provides the following benefits:
 * When building at a workshop or crafting at a crafting station inside a settlement, you can use the inventory of all linked workshops/crafting tables (though the shared items will not all show up in the workspace, they will automatically be used when crafting/building).
 * Linked settlements can share resources. This means, for example, if you have a surplus of food at one settlement, you can link it to a settlement with a food shortage.

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

To review existing supply lines, open the world map and press [C] 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 you ever want 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.
 * If a Provisioner dies while en-route between settlements, another member of the same settlement will take their place automatically, so the supply line is not broken.
 * 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 you connect 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.