How about: worlds with Atm 5, 6 or 8, and/or with Starport A, roll Pop on 1D+4.
Other Atm with Starport B or C roll Pop on 1D+1.
All other worlds roll Pop on 1D-1.
As another alternative, I like the Mongoose rule that relates starport to population. The table is inverted from CT so that A is 12, etc. You can then roll Starport using (2D-2+Pop).
So then you could roll "garden" planet pop on 1D+4, other worlds on 1D-1, and roll for starports after pop.
Other Atm with Starport B or C roll Pop on 1D+1.
All other worlds roll Pop on 1D-1.
As another alternative, I like the Mongoose rule that relates starport to population. The table is inverted from CT so that A is 12, etc. You can then roll Starport using (2D-2+Pop).
So then you could roll "garden" planet pop on 1D+4, other worlds on 1D-1, and roll for starports after pop.