Adam Clarke on Joshua 17:15

If thou be a great people - Joshua takes them at their own word; they said, Jos 17:14, that they were a great people; then said he, If thou be a great people or seeing thou art a great people, go to the wood country, and clear away for thyself. Joshua would not reverse the decision of the lot; but as there was much woodland country, he gave them permission to clear away as much of it as they found necessary to extend themselves as far as they pleased.