Transporter coordinates were a series of reference numbers used by a transporter system to determine the location to which a target was either to be beamed from, or beamed to. Coordinates could be automatically obtained by locking onto a communications signal or by tying into ship's sensors. They could also be manually input into the transporter console. (TOS: "A Piece of the Action", "Day of the Dove", "The Mark of Gideon")
In the mid-23rd century, transporter coordinates consisted of three groups of three numbers each. (TOS: "The Mark of Gideon") On the planet Gideon, the ruling body's council chambers were identified by the coordinates 875-020-709. A near-exact duplicate of the USS Enterprise built by the Gideons as part of a plot to kidnap Captain Kirk were identified by the coordinates 875-020-079.