Albert Barnes Commentary Numbers 35:8

"And concerning the cities which ye shall give of the possession of the children of Israel, from the many ye shall take many; and from the few ye shall take few: every one according to his inheritance which he inheriteth shall give of his cities unto the Levites." — Numbers 35:8 (ASV)

Nine cities were eventually given to the Levites from the large joint inheritance of Judah and Simeon; three were taken from the territory of Naphtali, and the other tribes gave four apiece.