Commentaire sur Les Nombres 34:4

ונסב לכם הגבול מנגב למעלה עקרבים — AND YOUR BORDER SHALL TURN ABOUT SOUTHWARD OF THE ASCENT OF AKRABBIM - In every passage in this chapter where it says ונסב or ויצא, it tells us that the boundary line was not straight (i.e., did not continue in the same straight line) but in proceeding it projected outside this straight line. Here, the word means that the boundary line left the straight line and bent towards the north of the world (in a northerly direction) diagonally towards the west, and the boundary line passed by the south of the Ascent of Akrabbim. Consequently the Ascent of Akrabbim was within the boundary (cf. Rashi on Joshua 15:3).

ונסב לכם, at this point the boundary projects somewhat.

Bending towards the north. Meaning: It bends in the direction of the land of Israel, and the border broadens, resulting in the land of Israel narrowing, for as much as the border broadens into the land of Israel, the land of Israel becomes narrower.