Matthew Poole and continuators on Joshua 18:4

4 Give out from among you three men of each tribe : and I will send them, and they shall rise, and go thorow the land , and describe it according to the inheritance of them, and they shall come again to me.

Three, not One, for more exact observation both of the measure and quality of the several Portions, and for greater assurance and evidence of their care and faithfulness in giving in their Account.

Either One of each of these Tribes, who were yet unprovided for; or rather Two of all the Tribes, even of them who had already received their Portions; which was highly expedient, that in case it should appear that there was not a sufficiency for each of these Tribes who wanted their Portions, their Brethren might be more ready either to assist them in procuring more Land, or to part with some of their own Portion to them.

Which they might now safely do, because the Terror of the late War was yet upon the Canaanites, who were loath to rouse so near and potent an Enemy.