(5-10) They shall divide it into seven parts. — The several tribes were not permitted to choose their own portions. In Numbers 26:54-55, we read: “To many thou shalt give the more inheritance, and to few thou shalt give the less inheritance.... notwithstanding the land shall be divided by lot.” These words imply that there must be unequal portions of territory for larger and smaller tribes, but that the particular position of each tribe must be settled by the lot, whereof “the whole disposing is of the Lord.” We are not told how this rule was carried out in the case of Judah, Ephraim, and Manasseh, who received their inheritance first. Possibly a sufficient extent of territory was surveyed at first to provide three large allotments. The three tribes might then cast lots, first between Judah and Joseph for the northern or southern portions, and then between Ephraim and Manasseh for the two sections of the northern territory. This would carry out the instructions of Numbers 26. But see above (Joshua 15:1).
Joshua 18:5-10
5 And they shall divide it into seven parts: Judah shall abide in their coast on the south, and the house of Joseph shall abide in their coasts on the north.
6 Ye shall therefore describe the land into seven parts, and bring the description hither to me, that I may cast lots for you here before the LORD our God.
7 But the Levites have no part among you; for the priesthood of the LORD is their inheritance: and Gad, and Reuben, and half the tribe of Manasseh, have received their inheritance beyond Jordan on the east, which Moses the servant of the LORD gave them.
8 And the men arose, and went away: and Joshua charged them that went to describe the land, saying, Go and walk through the land, and describe it, and come again to me, that I may here cast lots for you before the LORD in Shiloh.
9 And the men went and passed through the land, and described it by cities into seven parts in a book, and came again to Joshua to the host at Shiloh.
10 And Joshua cast lots for them in Shiloh before the LORD: and there Joshua divided the land unto the children of Israel according to their divisions.