Strategic resources are placed first. The generator cycles through the following deposit sizes, generating a deposit of that size for each strategic resource, until the quota set by the galaxy size and resource setting is reached:
This gives an average of roughly 10 resources per 6 planets with that resource.
After this, luxury resources are placed in this order: Plants, Gems, Drugs, Artifacts. Testing suggests that there are always 7 of each luxury resource, distributed across 4 planets. The exception is if the generator runs out of planets to place resources on, since each planet can only have a single resource. In this case, any remaining luxury resources to be placed are simply discarded.
To give some concrete numbers, we will consider a Tiny galaxy; the number of each strategic resource, the number of types of luxury resources, and the number of stars all grow proportionally (except for Huge galaxies, since the number of luxury resource types cannot grow any further at that point).
Average number of planets needed to hold all resources:
Average number of planets (ignoring special home system generation):
|Density||Planets per system|
Cells in green indicate settings that are unlikely to discard resources regardless of the resource setting. Cells in yellow indicate settings that are likely to discard resources on "High" resources. Cells in red indicate settings that are likely to discard resources on "Normal" resources, and will likely not have any luxury resources at all on "High" resources!