The island of Mossdeep is covered in plants and flowers. Its weather is mainly sunny, and its winds are stable. This clear weather made Mossdeep the ideal location to build a space center to launch large rockets. In Mossdeep, there is a white rock which holds a special meaning to the people at the space center. They placed the rock outside of the space center as a symbol of their wish for their rockets to fly safely. After entering the Hall of Fame, the player can obtain a level 5RSE/1ORASBeldum from Steven's house.
Mossdeep was the ideal location to build a space center which launches huge rockets because of the stable weather conditions. The Space Center is successfully sending rockets into space. In Emerald, the Space Center plays a big part in the plot, where Team Magma attempts to steal rocket fuel while a rocket begins to launch into space. On the second floor, the player will meet with Steven and battle two Team Magma Grunts.
Visit the house nearest the stairway to the Space Center to meet a young woman who uses a Wingull to send letters to a friend in Fortree City. Talk to the Wingull and it will take flight, off to deliver another note. If the player return to Fortree and visit the Pokémon Breeder in the northeast house there, it will get a Mental Herb that his Wingull found in its travels.
In Pokémon Ruby and Sapphire, the population of Mossdeep City is 45. Despite it being on an island in the middle of the sea, its population is fairly large, and it is Hoenn's fourth most populous city.
In Pokémon Emerald, the population of Mossdeep City is 52, making it Hoenn's fourth most populous city.
According to the anime, Mossdeep City is located on Mossdeep Island. As mentioned in Judgment Day! and Clamperl of Wisdom, ferry services run between Mossdeep and some of its neighboring islands, as well as Lilycove City.
Mossdeep City was the setting of two flashbacks. In the first flashback, Steven arranged a meeting in his house with Ruby and Emerald, where the two learned about a meteor's impending impact with their planet. After telling the two about his father's plan and their awareness of opposition to it, Steven also gave Ruby and Emerald a Mega Bracelet each, as well as an additional Mega Bracelet to pass to Sapphire. In the second flashback, Ruby and Emerald were at the Mossdeep coastline after their meeting with Steven. Ruby then used Courtney's memory lighter to investigate Steven's potential enemy.