From Aroer - See on Joshua 12:2 (note).

From Aroer, that is on the bank of the river Arnon,.... A city belonging to Moab, from whence the description begins, the river Arnon, on which it was situated, being the border between Moab and the Amorites, Numbers 21:13,

and the city that is in the midst of the river; or "even the city"; meaning the same city of Aroer, it lying both on the bank of it, and in the middle of it, or it was a double city, as may seem from Isaiah 17:2; and so differently situated at that river:

and all the plains of Medeba unto Dibon; of these two places, see Numbers 21:30; between them lay a plain, which some take to be the plain of Moab; but it rather seems to be a plain that was between these two places, and, according to Joshua 13:17, Dibon itself was in a plain.

From Aroer, that is upon the bank of the river Arnon, and the city that is in the midst of the river, and all the plain of Medeba unto Dibon;

13:9 Medeba unto Dibon - Two cities anciently belonging to the Moabites, and taken from them by the Amorites, Numb 21:30, and from them by the Israelites; and after the Israelites were gone into captivity, recovered by the first possessors, the Moabites.

13:7-33 The land must be divided among the tribes. It is the will of God that every man should know his own, and not take that which is another's. The world must be governed, not by force, but right. Wherever our habitation is placed, and in whatever honest way our portion is assigned, we should consider them as allotted of God; we should be thankful for, and use them as such, while every prudent method should be used to prevent disputes about property, both at present and in future. Joshua must be herein a type of Christ, who has not only conquered the gates of hell for us, but has opened to us the gates of heaven, and having purchased the eternal inheritance for all believers, will put them in possession of it. Here is a general description of the country given to the two tribes and a half, by Moses. Israel must know their own, and keep to it; and may not, under pretence of their being God's peculiar people, encroach on their neighbours. Twice in this chapter it is noticed, that to the tribe of Levi Moses gave no inheritance: see Nu 18:20. Their maintenance must be brought out of all the tribes. The ministers of the Lord should show themselves indifferent about worldly interests, and the people should take care they want nothing suitable. And happy are those who have the Lord God of Israel for their inheritance, though little of this world falls to their lot. His providences will supply their wants, his consolations will support their souls, till they gain heavenly joy and everlasting pleasures.