Charles Ellicott Commentary Numbers 34:5

"and the border shall turn about from Azmon unto the brook of Egypt, and the goings out thereof shall be at the sea." — Numbers 34:5 (ASV)

And the border shall fetch a compass ... — Although the exact locations of some of the places that determined the southern border have not been positively ascertained, on the whole, there seems to be very little doubt that the boundary line ran along the valleys. These valleys form a natural division between the cultivated land and the desert, extending from the Arabah on the east to the Mediterranean on the west. The Brook of Egypt—i.e., the Wady-el-Arish—formed the western boundary until it reached the sea.