Legislative apportionment is defined by Black’s Law Dictionary as the determination of the number of representatives which a State, county or other subdivision may send to a legislative body. It is the allocation of seats in a legislative body in proportion to the population; the drawing of voting district lines so as to equalize population and voting power among the districts.
Reapportionment, on the other hand, is the realignment or change in legislative districts brought about by changes in population and mandated by the constitutional requirement of equality of representation.