Then your south quarter shall be from the wilderness of Zin along by the coast of Edom, and your south border shall be the outmost coast of the salt sea eastward:

Wesley's Notes

34:3 Your fourth quarter - Which is here described from east to west by divers windings and turnings, by reason of the mountains and rivers. The salt sea - So called from the salt and sulphurous taste of its waters. Eastward - That is, at the eastern part of that sea, where the eastern and southern borders meet.

Jamieson-Fausset-Brown Bible Commentary

3-5. your south quarter-The line which bounded it on the south is the most difficult to trace. According to the best biblical geographers, the leading points here defined are as follows: The southwest angle of the southern boundary should be where the wilderness of Zin touches the border of Edom, so that the southern boundary should extend eastward from the extremity of the Dead Sea, wind around the precipitous ridge of Akrabbim ("scorpions"), thought to be the high and difficult Pass of Safeh, which crosses the stream that flows from the south into the Jordan-that is, the great valley of the Arabah, reaching from the Dead to the Red Sea.

Matthew Henry's Concise Commentary

34:1-15 Canaan was of small extent; as it is here bounded, it is but about 160 miles in length, and about 50 in breadth; yet this was the country promised to the father of the faithful, and the possession of the seed of Israel. This was that little spot of ground, in which alone, for many ages, God was known. This was the vineyard of the Lord, the garden enclosed; but as it is with gardens and vineyards, the narrowness of the space was made up by the fruitfulness of the soil. Though the earth is the Lord's, and the fulness thereof, yet few know him, and serve him; but those few are happy, because fruitful to God. Also, see how little a share of the world God gives to his own people. Those who have their portion in heaven, have reason to be content with a small pittance of this earth. Yet a little that a righteous man has, having it from the love of God, and with his blessing, is far better and more comfortable than the riches of many wicked.