(covers information from several alternate timelines)
In 2328, David Trotti traveled from Gamma Towles II to Starbase 47 on board a transport ship. This information was part of a passenger manifest recorded in the commercial transport database and reviewed by Lieutenant Commander Data in 2370. (TNG: "Inheritance")
In an alternate quantum reality visited by Worf in 2370, Starbase 47 was the object of covert surveillance by the Cardassian Union, who had reprogrammed the Argus Array to observe this, as well as Deep Space 5, the Iadara colony and the Utopia Planitia Fleet Yards. (TNG: "Parallels")
Background information Edit
Starbases are usually depicted as planet-based facilities or large space stations capable of supporting and supplying numerous starships. In "Parallels", Starbase 47 was depicted as a subspace relay station. Relay Station 47 was seen in TNG: "Aquiel".