Charles Ellicott Commentary Numbers 3:23

"The families of the Gershonites shall encamp behind the tabernacle westward." — Numbers 3:23 (ASV)

Behind the tabernacle westward. — As the position of the twelve tribes regarding the tent of meeting had already been determined, so in this and the following verses the position of the priests and Levites is fixed. On the east side of the tent Moses and Aaron and Aaron’s sons were to encamp, on the south the Kohathites, on the west the Gershonites, on the north the Merarites.