Howdy.
Over in 'International Elections', I complained about trying to pry data out of bureaucrats where a jurisdiction used non-Census data for redrawing electoral boundaries:
https://uselectionatlas.org/FORUM/index.php?topic=256686.msg5589174#msg5589174
Does that ever occur in the U.S.A.? If a state or municipality tried to used non-Census data (such as registered voters, population projections, undercounts, student population) as part of redistricting - but refused to release the data to the public - could they get away with it? Or would hordes of lawyers descend on them like a Biblical plague?
It is quite legal to use different population bases for redistricting than the census count of persons. Hawaii excludes non-residents and Kansas makes adjustments for in-state university students.
Where the challenge would be is to prove that the data used for the alternative base is reliable and that there is a rational state purpose in using it. There might be a quite reliable survey done of the locations of trees, but a state could not redistrict on the basis of trees.
In the United States, use of registered voters would be problematic since many persons are not registered to vote. It might be quite legal if the US used a system like in Canada where the government enrolls voters immediately before elections (it might be somewhat different now that Canada is shifting away to having permanent registration rolls). But it is quite reasonable to have equal number of (potential) voters for each representative.
In a direct democracy, each voter votes for their own interests. They might choose to take into account the interests of their children and their neighbor's children, or a Canadian neighbor who has overstayed his tourist visa, but they are not required to do so. In a representative democracy, a representative is chosen to stand in place of individuals. Since the representative votes in place of the electors who voted for him, it makes sense that each representative should represent the same number of voters.
A state might choose to use citizen voting age population, but then they would have a problem determining the citizen voting age population, since the census does not have a citizenship question.
If a city or state wanted to use some alternative population base, they would be attacked in court. The plaintiffs would use the supposed unreliability of data as a legal point and a court might rule on that basis. But redistricting is inherently political, and judges are no less susceptible to political influences than us mere mortals.
