Numbers 26:54

To the large [tribe], increase their inheritance. To the tribe with the greater populace, they gave a larger portion. Although the portions were unequal, as everything was assigned according to the size of the tribe, they implemented the apportioning solely by lots, and the lottery was inspired by the Sacred Spirit, as stated explicitly in Bava Basra. Elozor the kohein was clothed in the Urim veTumim, and said, with the Sacred Spirit, “If tribe so-and-so is drawn, then border so-and-so will be drawn with it.” The [names of the] tribes were written on twelve notes, and the twelve boundaries on twelve notes. They were mixed into a container, and the leader placed his hand into it and removed two notes. There appeared, in his hand, the note with the name of his tribe, and the note with the boundary specified for it. The lot itself would cry out, exclaiming, “I am the lot drawn for the so-and-so boundary, belonging to tribe so-and-so,” as it is said, “by word of the lottery.” The land was not apportioned dimensionally, since some boundaries were superior to others, but by assessed value. A poor Kor area was equivalent to a superior Seah area, all according to the value [of the soil.]

To that tribe whose people are many thou shalt make their inheritance large, and to the tribe whose people are few thou shalt give a smaller inheritance; to each his heritage shall be given according to the number of his names.

TO THE MORE THOU SHALT GIVE THE MORE INHERITANCE. “To a tribe which was larger in population they gave a larger portion [of the Land than that given to the smaller tribes]. And although the portions were [thus] not equal, since they divided [the Land] according to the size of the tribe, they did so only by means of the lot [as commanded in Verse 55], and the lot [assigned the portions] by means of Ruach Hakodesh. ”, Note 64. This is Rashi’s language.
But the interpretation of our Rabbis about this verse is not so. Instead, they said in the Sifre: 132. “To the more thou shalt give the more inheritance. Supposing somebody came out of Egypt with ten sons, and when they entered the Land they were [only] five etc. [we apply to this case the verse, To the more thou shalt give the more inheritance; if on the other hand he had five sons when he came out of Egypt, and when they entered the Land they were ten, we apply to them the verse, and to the fewer thou shalt give the less inheritance]. ”, but upon the number that the family had when they left Egypt — hence if they became fewer, we still apply the verse: To the more … since they were more when they left Egypt, and vice versa. It is thus obvious that the Sifre applied these verses to the division of the Land among the fathers’ houses, and not, as Rashi explained it, to the division between the twelve tribes as a whole. And likewise it is explicitly stated in the Gemara that the meaning of [this section] according to the Sages was not to distinguish in any way between [the portion given to] each particular tribe [since they each received an equal portion], just as they have said: “It is well-understood according to the Sage who says [that the Land was divided] according to [the numbers of] those who came out of Egypt, why Scripture states, To the more thou shalt give the more inheritance etc.” etc. ; whereas if he had originally five sons etc. [as explained by Ramban above in the text]. But according to the Sage who says that the Land was divided according to the number of people at the time that they entered the Land, what is the meaning of the phrases: to the more and to the fewer, since each family received a share equal to its numbers at that time?” From this text, too, it is obvious that the Sages were not referring to differences between the portions of larger or smaller tribes, but instead applied this verse to …

לרב תרבה נחלתו, a reference to the amount of land, for although the land was being divided 12 tribes in shares of equal value in terms of money, the size of the allocations varied according to the quality of the soil each tribe received. A tribe who numbered many souls received a quantitatively larger piece of real estate as is spelled out here by the words לרב תרבו נחלתו, “you shall give a larger inheritance to the numerically superior tribe.”
This is the reason why Menashe and Ephrayim received 2 separate territories seeing that their father Joseph had been a firstborn and treated as such in Yaakov’s final blessing, they were entitled to two such shares. (Genesis 48,22) This is also the way we must understand Chronicles I 5,1 ובחללו יצועי אביו ניתנה בכורתו ליוסף בן ישראל, “and when he defiled the bed of his father his birthright was given to Joseph, son of Yisrael.”
Shimon, who numbered fewer people than any other tribe at this count, received a relatively small parcel of land, which itself was an enclave within the territory allocated to the tribe of Yehudah. (compare Joshua 19,9 on this subject) This also was the fulfillment of Yaakov’s wish in Genesis 49,7 “I will divide both Levi and Shimon among the tribes of Israel.”