Albert Barnes Commentary Numbers 34:3-5

"then your south quarter shall be from the wilderness of Zin along by the side of Edom, and your south border shall be from the end of the Salt Sea eastward; and your border shall turn about southward of the ascent of Akrabbim, and pass along to Zin; and the goings out thereof shall be southward of Kadesh-barnea; and it shall go forth to Hazar-addar, and pass along to Azmon; and the border shall turn about from Azmon unto the brook of Egypt, and the goings out thereof shall be at the sea." — Numbers 34:3-5 (ASV)

The southern boundary began at the Dead Sea. The broad and desolate valley by which the depressed bed of that sea is protected to the south is called the Ghor. A deep, narrow glen enters it at its southwest corner; it is called Wady-el-Fikreh and is continued in the same southwestern direction under the name of Wady el-Marrah, a wady which disappears among the hills belonging to “the wilderness of Zin”; and Kadesh-barnea (see Numbers 13:26 note), which is “in the wilderness of Zin,” will be, as the text implies, the southernmost point of the southern boundary.

From there, if Kadesh is identical with the present Ain el-Weibeh, westward to the river, or brook of Egypt (now Wady el-Arish), is a distance of about seventy miles. In this interval were Hazar-addar and Azmon. The former was perhaps the general name of a district of Hazerim, or nomad hamlets , of which Adder was one; and Azmon is perhaps to be identified with Kesam (the modern Kasaimeh), a group of springs situated in the north of one of the gaps in the ridge and a short distance west of Ain el-Kudeirat.

(Others consider the boundary line to have followed the Ghor along the Arabah to the south of the Azazimeh mountains, from there to Gadis around the southeast of that mountain, and from there to Wady el-Arish.)