According to the Vilna Gaon
After Yechezkel received through prophecy the vision of the Third Bais haMikdash with its details (Chapters 40-44), he receives a command about the future division of Eretz Yisrael among the tribes (chapters 45-48).
After defining the boundaries, Yechezkel tells that the land is divided into 13 parallel equal portions running from the east to the west. The order is from north to south: Dan Asher, Naftali, Manasseh, Ephraim, Reuven, Yehudah, Binyomin, Shimeon, Yissachar. Zevulun and Gad. In between the portions for Yehudah and Binyomin, is a “holy portion of land” comprising the Bais haMikdash area, the domains of the Kohanim, Leviim and representatives of the rest of the Jews and of the Nasi.
Each portion consisted of a strip of land 25,000 broad. According to Kimchi this measurement is in amos; according to Rashi, this measurement is in reeds (standard measurement of six amos).
According to most the western border of each stripe would be the Mediterranean Sea. The eastern border would be trench below sea-level through which the Yarden river flows from the Galilee Sea to the Dead Sea and extends north and south. Some learn that the portion was a square of 25,000 by 25,000 (Sifrei). Another Sifrei mentions that the strips have no western or eastern limit, but extend to the “ends of the world.”
The commentators note that people who converted, embraced Judaism and had descendants received an equal portion of land as the other Jews. A portion of land was assigned for them in the territory of the tribe among which they lived.
LAND OF THE NASI
Holy section is in the middle of the strip for the Nassi. The land of the Nasi is located on either side of the Holy section. This section is the same size as the other 12 strips of land, just broken into three sections.
