Asteroid Smart Spawn
Solution:
1) For each asteroid spawn, the map maker sets an adjustable radius.
2) The editor decides on a numerical cut-off point for that area.
3) As long as the number of asteroids in the area (X) are less than the cut-off point (Y), the spawner continues to spawn them.
4) Once X = Y, the spawner stops.
Bonus points:
The rate at which the spawner spawns asteroids gets slower as X -> Y, with an asymptote at Y.