Crane's map is a paper note in the Fallout 76 update Wastelanders.
Background
Created by Crane before he succumbed to the Scorched Plague, Crane's map is a hand drawn sketch of the interior of Gauley Mine, showing where the entrances and storages are. The map shows the passcode to the locked door to be 071990.
Location
The note can be found on the body of Crane after he is killed either by the player character or Sol during The Elusive Crane.