Rashi: The entire land will be converted to a flat plain. The mountains will be lowered, and the entire world will be a plain. Only Yerushalayim will be a mountain, so it will be seen higher over everything.

Radak: Now, all around Yerushalayim are mountains - "Yerushalayim Harim Saviv Lah" (Tehilim 125:2). It will become flat, and Yerushalayim will be raised and elevated above the entire land. Even though already now it is higher than all of Eretz Yisrael, due to the mountains around it, its height is not so apparent. Then, all around it will be flat, so its height will stand out. Yeshayah said "Nachon Yihyeh Har Beis Hashem b'Rosh Harim v'Nisa mi'Geva'os" (2:2). Even though there, v'Nisa means that it will be elevated in grandeur and level, both of these are true (it will also be higher altitude).

Malbim: After Har ha'Zeisim splits, the canyon between the two halves will become a plain.

Rashi citing Tosefta Sotah 11:7: Negev Yerushalayim is a plain. Geva Rimon is a rocky land. From there (a place of mountains), it will begin to flatten out and resemble south of Yerushalayim, which is a plain.

Malbim: The plain will be from Geva, which is south of the current Yerushalayim, until Rimon, which is by the future Yerushalayim that Yechezkel saw, south of the current one.

Rashi: Yerushalayim will appear high, because all around it will be a plain. Radak - the Aleph is in place of a Vov, the middle letter of the root. It is like the Aleph in "Kam Sha'on" (Hoshe'a 10:14), but there the Aleph is silent. Malbim - both the new Yerushalayim, and the Mikdash, which will be where the old Yerushalayim was, will be elevated.

Rashi: It will be in its [initial] place. Radak - however, it will elongate and widen.

Rashi: Also it is in its place. From there, the length of the city will extend until "Yikvei ha'Melech." Radak - Sha'ar ha'Pinim is "Sha'ar ha'Pinah" in Yirmeyahu 31:37. "Migdal Chananel" is the same as there.

Malbim: The old Yerushalayim was from Sha'ar Binyamin until Sha'ar ha'Rishon. The new Yerushalayim will be from Sha'ar ha'Pinim and Migdal Chananel until Yikvei ha'Melech.

Targum Yonasan: Sichei Malka. Rashi - these are pits of the king. Also 'Sichin u'Ma'aros' (Bava Kama 50b) are pits. Every Yekev in Tanach is a pit in front of the winepress; the wine flows into it. Radak - this is like "Goren va'Yekev" (Hoshe'a 9:2). It was known that they are outside the city.

Rashi citing Yalkut Yeshayah 472: This is the Okainus. Yerushalayim will reach until the end of the world - pits that the King, the King of kings, carved out.