Whereabouts was Edom in relation to Eretz Cana'an?
Rashi: Edom was situated on the eastern tip of the southern border of Cana'an, at the foot of the Yam-ha'Melach,
with Mo'av beside it on its east.
Which served as the south-eastern extremity.
The Ha'amek Davar, who queroes Rashi on this point, since we now know that Edom lay on the eastern edge of the southern border of Cana'an