What is the connection between Hor ha'Har and the western border?
Rashi: Hor ha'Har, which was situated at the north-western tip of Eretz Yisrael, 1 rose out of the sea at its northernmost tip, so that part of it was actually in the sea and part of it outside.
Da'as Zekenim (4), Hadar Zekenim (4): This is not to be confused with the Hor ha'Har on which Aharon died, as there were two places named Hor ha'Har. Moshav Zekenim: Aharon died south of Eretz Yisrael, on the border of Eretz Edom. The Hor ha'Har here was situated on the northern border of Eretz Yisrael; the Gemara in Gitin 8a, calls it "Turei Amnon".
What does "Tesa'u lachem Hor ha'Har" mean?
Rashi: "Tesa'u ... " means 'You shall turn 1 to Hor ha'Har' - from the west to the north.
Rashbam, Targum Onkelos and Targum Yonasan: It means 'make the border Hor ha'Har'.
Our verse implies that Hor ha'Har is in Eretz Yisrael. Moshe and Aharon did not enter the land, yet they came to Hor ha'Har (20:23)!
Da'as Zekenim (4), Hadar Zekenim (4): There were two places named Hor ha'Har. Moshav Zekenim