In my world, toponomy is still being developed, but a few conventions have already been made:

City Rank
In the Savrinian culture, larger town get an honorary suffix from the Imperial Population Commission:
-trivan : town (5.000 - 15.000 inhabitants)
-jurmos : larger town (15.001 - 25.000 inhabitants)
-ardan : small city (25.001 - 50.000 inhabitants)
-muros : city (50.001 - 125.000 inhabitants)
-van : metropole (over 125.000 inhabitants)
-irvan : capital (given to the capital)

basic rules
1. 'Locative town' : Bedbasirvan ==> Bedba (rock) -zi- (loc. sg.) -irvan (capital) : Capital on the rock
2. 'Gentive town' : Amvaimuros ==> Amva (ancient sea godess) -i- (gen. sg.) -muros : City of Amva