Game World
The game's world will consist of a grid of tiles, rendered in a top-down 2D environment. The world storage will be "sparse", eschewing the storage of any "empty" tiles, allowing for station sizes limited only by the precision of the internal coordinate representation (single-precision floating point limits us to ~1 million tiles on each axis).
Aliens will enter and exit the world via spaceships that spawn into the game and then dock to appropriate locations around the station. The game will need to support these ships spawning and moving outside of the limits of the tile map.
NB: We will try to structure the code in such a way that converting to rendering this 2D world using 3D models will be doable, however this is not a strict goal and it's okay if we wind up "stuck" with 2D sprites.