Game Design
Level Design
Game Theory
Misc Art Button
3D Models

Open world level design is unique because you have less control over player intent. Inspire curiosity when designing your world so that interesting landmarks taunt the player to explore from great distances. Locally, there is probably a large number of things the player may want to be doing in each sector but you must build so any of these things will play right. You must also communicate with other designers to assure gameplay seams well with missions and objectives in bordering sectors.