The newest iteration in the Far Cry series is set to have a map editor available at launch, which will include all kinds of fun stuff to play around with. Players will be able to create maps however they'd like by terraforming land, and then placing assets like buildings and items. Some of these will look familiar, but not "Far Cry 5" familiar.
Far Cry 5's map editor is set to include memorable things from all kinds of Ubisoft games. Items from the following games have all been confirmed: Far Cry 4, Far Cry Primal, Watch Dogs, Assassin's Creed IV: Black Flag, and Assassin's Creed Unity. This will account for the beginning 9,000+ items available in the map editor. Ubisoft has plans to bring even more later, with six already planned updates. These will bring items from Far Cry 5's add-ons, which will include things from Vietnam, zombie-related artifacts, and sci-fi stuff.
All the cool items aside, Far Cry 5's map editor will allow you to create all kinds of custom maps. After creation, these maps will be usable in single player, cooperative, and competitive modes. There will also apparently be some Ubisoft specifically created maps releasing later.
The map editor in Far Cry 5 is all a part of the Far Cry Arcade system. This will come with its own website that will have map listings, profiles, and most likely mods. There will also be weekly Arcade events.
Source: Rock, Paper, Shotgun