Rapczak said. “It’s not procedurally generated it. There are 700 unique islands spread across the map with different biomes. There’s also sort of story islands and PVE islands where some of the game’s backstory and lore and crazy mythological creatures can be found.” Source: https://variety.com/2018/gaming/news/atlas-studio-wildcard-interview-1203085907/ If you got something better I'm all ears. Otherwise...
Correct, it is not procedurally generated. Every island is hand-made by the artists and level designers using tools like World Machine, Houdini and custom UE4 blutilities. Completed islands are then hand-placed in the world map using our world layout tool (will be available to end users).