As for the Jebusites, the inhabitants of Jerusalem, the children of Judah couldn't drive them out: but the Jebusites dwell with the children of Judah at Jerusalem to this day.
Ancient Near Easterners used natural landmarks (rivers, mountains, deserts, towns, etc.) to construct borders as well as artificial boundaries that they made by drawing lines between sites. Virtually all nations have used these methods, and they are still common today.