“ Appoint for yourselves three men for each tribe, and I will send them and they will arise and walk through the land and describe it according to their inheritance, and they shall come to me, and they will divide it into seven portions. Judah shall abide in his border on the south, and the house of Joseph shall abide in their border on the north, and you shall describe the land into seven portions and bring it here to me, and I will cast lots for you here before YHWH your God.”
“Three men” might mean literally three, or it may mean ‘a few' as so often with ‘three'. But the onus was thrown on the tribes for selection. As a wise leader Joshua wanted them involved in all the decisions so that then they would feel that they were theirs and would be more enthusiastic. But it was Joshua who would send them. Their final instructions and guidance would come from him. He did not want them to make mistakes and make the future more difficult by carelessness.
“And they will arise and walk through the land.” This would pose no difficulties for a few sensible travellers. They could take on various guises and routes were already well travelled by strangers and traders of all kinds passing through the land. Not that there would not be dangers. There were always dangers when travelling. That was why they needed careful instruction and guidance from an expert.
“And describe it (write it down) according to their inheritance.” Writing was a familiar art to any educated Israelite (Judges 8:14). Careful records had to be made by these surveyors so as to divide up the remaining land of their inheritance accurately and in accordance with the situations in each. They were to divide it up into seven sections, which would then be allocated by lot in the sight and presence of God at the Tabernacle.
“I will cast lots for you.” For the princes as representing the people.