Asteroid field

Size as a world
Asteroid fields are much smaller then planetary bodies and thus contain much less buildings. While a planet may have 20-100 building spaces, asteroids can commonly contain less then 20, with only few exceeding 30. Minimalist levels are 8 buildings, and these fields can contain 2-3 slides. However, asteroids do contain as much as double the oribtal space.

Difference from planets
Aside from the obvious size and therefore production difference, limiting the ability of production, asteroid fields contain lots of raw materials which are more easily extracted then from planets alone. They also have much larger 'oribtal' space around themselves offering themselves up as more defensive territories then worlds, in some cases, capable of double the defencive structures of even the largest of planets.