Verse Nu26-52:56 states
And the LORD spoke unto Moses, saying:
'Unto these the land shall be divided for an inheritance
according to the number of names.
To the more thou shalt give the more inheritance,
and to the fewer thou shalt give the less inheritance;
to each one according to those that were numbered of it
shall its inheritance be given.
Mostly the land shall be divided by lot;
according to the names of the tribes of their fathers they shall inherit.
According to the lot shall their inheritance be divided between the more and the fewer.'
From the underlined words Rashi infers that
The land was divided according to the number of people
per tribe (that is, each tribe did not get one twelfth of the land but
rather received a parcel of land proportional to its numerical size).
Similarly the land was divided by dollar value not by area. So for example
two tribes with equal numbers of people could inherit two different size
landplots if both had equal worth.
We see here that the essence of the Rashi comment are details
on numerical computation.