Mordan IV was the inhabited fourth planet of the Mordan system. This was the homeworld of the Mordanites, a spaceflight humanoid species. The Mordanite government was led by a governor. In 2364, that role was filled by Karnas.
Traditionally, the population of Mordan was made up of a number of different tribes, each with its own leader. In 2319, the leader of one of the tribes was assassinated by his enemies from another tribe. His son, Karnas, was determined to avenge his father's death. To this end he took hostage the 63 passengers aboard a starliner, and demanded weapons from Starfleet in exchange for their release. Two negotiators were sent in by Starfleet, and both of them were killed. Then Captain Mark Jameson was dispatched to Mordan, successfully negotiating the release of the hostages. Unknown to Starfleet, Jameson had given Karnas the weapons he wanted, but troubled by his breaking of the Prime Directive, he also gave weapons to Karnas' enemies. This caused a bloody civil war between the two factions, which ended in Karnas becoming leader of Mordan in 2359.
Much of the original capital city was destroyed during the civil war, only the tunnels beneath the city surviving intact. Five years later, the Federation ambassador, Hawkins, was taken hostage by Karnas in an attempt to lure Jameson to Mordan. Karnas blamed Jameson for the forty years of civil war. He initially blamed the kidnappings on terrorists, but Jameson realized that Karnas was responsible. He mounted a failed rescue attempt, and when Karnas requested his life in exchange for the hostages, he agreed. Jameson died in front of him due to an age-reversing drug he had taken, but Karnas was satisfied he was dead, and released the hostages. (TNG: "Too Short a Season")
Mordan IV cityscape maquette
A view on Mordan IV city and its surrounding landscape was proffered from Karnas's office, though only barely. The near indiscernible, almost throw-away visual, belied the rather substantial effort, that went into its creation. It was not even a matte painting, the method of choice in the franchise for creating long-view landscape visuals of vistas, but rather a cityscape maquette, combined with a background landscape painting. One of its creators, Mike Okuda has noted in this respect, "Creating models wasn't really our job. We weren't set up for model making in the art department, and we were lucky enough to have the services of Paramount's effects shop, as well as talented outside vendors like [professional model makers] Greg Jein and Tony Meininger. But we tried to help out when the vendors were too busy, or if it was something small that we thought was cool but the budget didn't allow. Mostly we painted a few found objects and a tabletop to create a loose impression of a cityscape. I recall that we used a big wok for the dome of one large building." (Star Trek: The Next Generation 365, p. 43) In regard to the Mordan IV cityscape maquette, he had further remarked, "Rick made most of the model city buildings. He used hot melt glue to create some cool sculptural detail on the skyscrapers. Very simple, but it looked good when photographed. I did paint and tape detail on dome structures what were mostly made from found objects. I recall that one big dome was a cooking wok. Later, I borrowed the shapes of the buildings for the animated city map graphic on the main viewer." 
The graphic, Okuda referred to, was the LCARS silhouette display on the main viewscreen of the USS Enterprise-D, consulted by the crew in the episode. Utilizing the same background painting, the Mordan IV maquette was only the second such model used in the Star Trek: The Next Generation series, after the Farpoint Station landscape maquette, used in the pilot "Encounter at Farpoint". Superseded by matte paintings, it would remain so for years, until the season six episode "Birthright, Part I", for which a maquette of a Romulan prison camp would be created. (Star Trek: The Next Generation Companion, 3rd. ed., p. 43) Due to the size of maquettes, like that of Mordan IV, they are almost always scrapped after use, this one no exception. Yet on rare occasions, parts of them are re-utilized for use in another capacity. One of the transparent domes turned up as Alexandra's toy in Toya's quarters aboard the USS Enterprise-D in the later first season episode "When The Bough Breaks".