The Department of Cartography was a department inside the Federation government that managed the distribution of information concerning traffic patterns, navigational anomalies, and other unusual phenomena inside Federation space.
In 2375, Luther Sloan posed as "Wendell Greer", an assistant director of the Department of Cartography, in order to attend a joint Federation-Romulan conference about the Dominion War, on Romulus. (DS9: "Inter Arma Enim Silent Leges")
Per the Star Trek Encyclopedia, 4th ed., vol. 1, p. 263, additonal duties of this agency included the "collection, maintenance, and distribution of map products within the Federation."
In the first draft script of DS9: "When It Rains...", Julian Bashir and Miles O'Brien traced a burn-back to a computer in the Department of Cartography, at Federation Headquarters. The source of the burn-back had the screen name "W.G.", suggesting it was Sloan, using his "Wendell Greer" pseudonym again.