What is "Achuzas ha'Ir"?
Rashi: Surrounding the city, an inheritance of a Chulin residence, for Yisrael to build houses.
Radak, Malbim: All will have in inheritance in Yerushalayim. Every Shevet will have a gate, like it says at the end of the Sefer.
Where will this be?
Rashi: It will be south of the second 1 .
I.e. the Leviyim's portion, which is second to the Kohanim's. (PF)
What is the significance of its size and place?
Rashi: It is as long as the first two (25,000). Together with the first two, they will form a square 25,000 wide.
Malbim: It is south of Achuzas ha'Leviyim, for the city will be in the south.
Why does it say "Le'umas Terumas ha'Kodesh"?
Rashi: It is the same length as the strips of Terumas ha'Kodesh (Radak ? i.e. the Achuzos of the Kohanim and Leviyim).
How is it for all Beis Yisrael?
Rashi: It is for residence of Zarim.
Refer to 45:6:1:2.