You are confusing land and housing - they are not the same. Land area is fixed but habitable space is not. In built up areas the constraint on building new housing is largely regulatory (mostly planning regulations).

I lump land and housing together because that's how reality does it. Aside from trailer-houses they all stay on one piece of land for the duration.

If an analysis depends on houses being able to fluidly change land positions I don't think it would be very useful.