New Defender's Study Bible Notes
18:4 three men for each tribe. Five of the tribes had already been awarded their lots (Judah, Ephraim, Manasseh, Reuben, Gad), so presumably only the seven tribes remaining were represented on this committee. It is obvious that the seven subdivisions which they described were not equal in geographical area, so they presumably tried to take other factors into consideration in arriving at their optimum divisions.
18:8 describe the land. They were to survey and divide the land.
18:9 seven parts in a book. The scientific art of surveying is very ancient. The Egyptians had practiced it, but long before that the sons of Noah and their descendants used it to divide the lands for their nations in the earth after the Flood (Genesis 10:32).
18:11 children of Benjamin. The portion that fell to Benjamin was adjacent to Judah on the north, with the city of Jerusalem (still occupied by Jebusites) right on the boundary between. Benjamin, of course, later remained with Judah when the nation of Israel was divided at the time of Rehoboam (I Kings 12:20,21).