Which Midbar does the verse discuss?
Rashi: It is Midbar Kadesh, which is Midbar Tzin, by Edom, at the southeast corner (of Eretz Yisrael); through there, they entered Eretz Yisrael
Yisrael passed from the border of Edom to the border of Mo'av, and conquered Sichon and Og (Shoftim 11:16-22), and afterwards entered Eretz Yisrael! Rather, Moshe's spies entered from Midbar Tzin (Bamidbar 13:21); it is also called Kadesh Barne'a (Devarim 1:19, Yehoshua 15:7). (PF)
In which direction are the Pras River and Yam ha'Gadol?
Rashi: The Pras is in the north[east], and Yam ha'Gadol 1 is in the west.
Radak: It is called Yam ha'Gadol because it is bigger than the other seas of Eretz Yisrael, i.e. Yam ha'Melach and Yam Kineres.
What is "ha'Levanon ha'Zeh"?
Radak #1: It is a known place in Eretz Yisrael. Even though it is across the Yarden, it is visible (from when Bnei Yisrael were), therefore it says "ha'Zeh". Also Moshe said "ha'Har ha'Tov ha'Zeh veha'Levanon" (Devarim 3:25).
Why does it mention Eretz ha'Chitim?
Radak: It is because they lived in that corner.