An unbroken line of cases from Reynolds v. Sims to Board of Estimate v. Morris, 109 S. Ct. 1433, 1437 (1989), establishes a "general rule of population equality between electoral districts."  With similar consistency, these cases recognize that, in applying this rule, "more flexibility may * * * be constitutionally permissible with respect to state legislative apportionment than in congressional districting."  Gaffney, 412 U.S. at 743-744.  Accord Mahan v. Howell, 410 U.S. 315 (1973). . . .    

The rule of population equality "is a principle designed to prevent debasement of voting power and diminution of access to elected representatives." Kirkpatrick v. Preisler, 394 U.S. 526, 531 (1969).  Population equality will not always accommodate the twin goals of equality of representation and equality of voting power in precisely equal measure, because the population of a district changes, the figures on which apportionment is based are inherently imprecise, and the inhabitants of a district who at the time of apportionment may not be citizens or eligible to vote may become eligible voters before reapportionment occurs.  Gaffney, 412 U.S. at 744-746 & 745 n.10.  That is the reason for the second principle, which recognizes that "(m)athematical exactness or precision is hardly a workable constitutional requirement." Reynolds, 377 U.S. at 577 (quoted in Gaffney, 412 U.S. at 743). 

This Court has explicitly recognized on two occasions that a population basis for districts does not precisely equalize voting power.  In Gaffney, the Court observed that even though decennial apportionments are based primarily on census figures, "(t)he proportion of the census population too young to vote or disqualified by alienage or nonresidence varies substantially among the States and among localities within the States." 412 U.S. at 746-747.  The Court noted that the 1970 Census, for example, showed that "New York has a 29% variation in age-eligible voters among its congressional districts, while California has a 25% and Illinois a 20% variation."  Id. at 747 n.13.  Notwithstanding this recognition, the Court did not even remotely intimate that the practice in these States of apportioning districts on the basis of population violated the Fourteenth Amendment, as petitioners now contend.  On the contrary, the Court cited the inherent imprecision in population-based apportionment as the reason why "(f)air and effective representation * * * does not depend soley on mathematical equality among district populations.  There are other relevant factors to be taken into account and other important interests that States may legitimately be mindful of." Id. at 748-749 (footnote omitted).* 

The Court applied the same common-sense approach in Burns v. Richardson, 384 U.S. 73 (1966). There, the State of Hawaii used registered voters as an apportionment base, producing a result that differed significantly from that which would have resulted from population-based apportionment.  Id. at 90.  The Court rejected plaintiffs' contention that the deviation from total population was inconsistent with Reynolds.  Indeed, this Court relied on Reynolds to hold that a state may legitimately choose any one of three apportionment bases -- eligible voters, citizen population, or total population.  Burns, 384 U.S. at 91.  The Court reasoned that for purposes of apportionment "(t)he decision to include or exclude (aliens, transients, short-term or temporary residents, or persons denied the vote for conviction of crime) involves choices about the nature of representation with which we have been shown no constitutionally founded reason to interfere." Id. at 92.** 

The remedy adopted by the courts below was based on California's choice to use population to apportion legislative districts.  Pet.  App. A20.***  The remedy was therefore fully faithful not only to the rule of population equality but also to this Court's teaching that courts generally must respect a State's legislative judgments regarding apportionment.  E.g., Wise v. Lipscomb, 437 U.S. 535, 540 (1978). 

Moreover, petitioners' position would create an indefensible tension between the rules governing congressional apportionment and those governing state legislative apportionment.  As the panel majority recognized (Pet. App. A19-A20), Wesberry v. Sanders, 376 U.S. 1 (1964), held that under Article I, Section 2, total population is the only appropriate apportionment base for congressional apportionment.  In petitioners' view, what is constitutionally required for apportionments for the House of Representatives is constitutionally forbidden in apportionments for state and local legislative bodies.  Petitioners have pointed to nothing that would sanction such a curious result.****
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* Petitioners and the [Judge Kozinski] dissent from the panel opinion insist that the Fourteenth Amendment must be construed to confer primacy on either the principle of equal representation or that of equality in voting power.  Pet. 6-10;  Pet. App. A34.  On the contrary, Burns and Gaffney make clear that the State is free to strike a reasonable balance between these principles based on legislative judgments.  Those two decisions also make clear that, contrary to the petitioners' and the dissent's assertions, the Court has addressed the fact that the rule of population equality does not ensure precise equality of representation. 

** The Court has subsequently made clear that various state interests, including the desire to equalize voting strength, may justify small deviations from population equality.  Karcher v. Daggett, 462 U.S. 725, 740-741 (1983).  But, at the same time, Karcher reaffirmed that equal representation for equal numbers of people is still the basic constitutional imperative.  Id. at 730.  

* * * Most states, like California, require that legislative apportionment be based on population.  [Citing laws of 26 States.] 

* * * * The dissent mistakenly relies (Pet. App. A41 n.15) on the statement in Reynolds that arguments based on the "federal analogy" are "inapposite and irrelevant to state legislative redistricting schemes." 377 U.S. at 571-577.  Reynolds was referring to those parts of the federal plan that compromised the principle of equality to the principle of state sovereignty, i.e., the provisions that each State would have two Senators and at least one Representative.  In contrast, Reynolds found support for its decision in that part of Article I, Section 2 that provides for equal representation for equal numbers of persons.  The interpretation of that Clause is therefore highly relevant here.