Many countries, especially those very large in size and/or having a federal system rather than a unitary system, delegate the responsibility for drawing national legislative districts to regional entities such as states or provinces. For example, in the United States, seats in Congress are allocated to the states on the basis of each state's relative population. Each state is then responsible for drawing the prescribed number of congressional districts within its borders. Australia and Canada use a similar system of allocating seats in the national parliament to the states or provinces and then having independent electoral commissions in each state or province draw district boundaries.
In the United States, the decennial process of allocating congressional seats among the states is called 'reapportionment.' In Canada, the decennial reallocation of Parliamentary seats among the provinces is known as 'redistribution.' But in many countries, no special terminology is applied to this allocation process. This is especially true of countries that are not federal systems, as are the United States and Canada, or countries where regional entities have little power over redistricting decisions.
Population (either census enumeration data or voter registration figures) is almost always used as the basis for apportioning seats to national legislatures. In fact, the stated purpose of decennial census in the United States is to determine the proper allocation of congressional seats among the states. The U.S. Constitution, in Article I, Section 2, provides that:
Representatives shall be apportioned among the several states...according to their numbers....The actual Enumeration shall be made within three years after the first meeting of the Congress and within every subsequent term of ten years in such manner as they shall by law direct.
Before seats are allocated, however, the total number of seats in the legislative body is often determined. But this is not always the approach adopted. In its first 120 years, for example, the U.S. House of Representatives simply grew in size to accommodate new states and a rapidly growing population. From 1790 to 1900, seats were allocated to states on the basis of a population quota which, despite its gradual increase over time, resulted in the House of Representatives expanding in size from 106 to 391 during this time period.
Many countries still allow the legislature to grow as the population of the country increases. In the United States, however, a permanent ceiling on membership in the House of Representatives was set at 435 legislators in 1910. Seats were allocated by first giving each state one seat and then awarding the remaining seats in succession to the states with the largest remaining quota. In 1950, the statute defining the formula was modified slightly. Each state was given one seat, and the remaining 385 seats were allocated in succession under a priority numbers formula. This formula is referred to as the 'method of equal proportions' or the Huntingdon method.
Although the process is a mechanical one, the formula for the allocation of seats has not escaped controversy. Since 1790 states in the United States have argued over how congressional seats are apportioned, and states that have lost representation have been especially sensitive about the process.
Some countries have adopted solutions designed to alleviate this problem. Canada, for example, has solved this problem by never allowing the number of seats allocated to a province in the House of Commons to decrease. Canada, like the United States, requires that the distribution of seats in the House of Commons be governed by the 'proportionate Representation of the Provinces,' based on a decennial census. However, a 'grandfather clause' was adopted to protect provinces with declining populations relative to the other provinces. This clause, first enacted in 1976 and then re-enacted in different legislative form nine years later, ensures that no province can ever have fewer electoral districts than it had in 1976. The size of the House of Commons has gradually increased as a result. (For more information on the redistribution process in Canada, see the case study Representation in the Canadian Parliament, and for a table displaying the results of the latest Canadian allocation of seats to the provinces, see Canadian redistribution formula using 1991 census figures.)
There are two problems with allowing states or provinces to retain more seats than population alone would dictate:
- the size of the legislature could become unwieldy;
- the electoral quota (the population of the state divided by the number of seats allocated to the state) can vary considerably across states or provinces.
The latter occurs when a state or province is awarded a greater number of seats than it would normally be entitled, based on its relative proportion of the population. In Canada, these are referred to as 'add-on' seats. In Canada, for example, the provincial population quota varied from 32,441 for Prince Edward Island to 97,912 for Ontario in the 1980s as a result of add-on seats for Prince Edward Island.
But a broad range in population quotas is possible even without add-on seats. In the most recent round of congressional redistricting in the United States in 1991, the population quota for congressional districts ranged from 455,975 in Wyoming to 803,655 in Montana. This broad range occurred because each state is awarded at least one seat, even if its population is below the 'national quota' for a seat. No national electoral quota is actually applied in the United States; quotas are calculated only on a state by state basis. The population of the state of Wyoming was below the 'national quota' for a congressional district, but was awarded a seat; whereas the population of Montana, more than ample for one congressional seat, was not quite large enough to be allocated two seats.
