Countries that have recently established or reformed their redistricting practices have often instituted a set of formal rules, or criteria, for their boundary authorities to consider when drawing electoral districts. Although this is especially true in countries that have adopted neutral boundary commissions, many countries that allow the legislature or a government agency to redistrict have enacted redistricting criteria as well. These rules are usually listed in the electoral law, but they can sometimes be found in the country's constitution. Examples of redistricting rules enacted by selected countries can be found in Election laws or constitutional provisions listing redistricting criteria for selected countries.
The rules often specify that districts should be as equal in population as possible, taking into account a variety of other factors. Administrative and/or natural boundaries and other geographic features such as sparsely populated or isolated territory are factors commonly listed. Respect for communities of interest is another factor many countries specify. In some countries, especially developing countries, redistricters are asked to consider the predominant means of transportation and/or communication as well.
Almost all countries that have formal redistricting criteria require that districts be as equal in population as possible. Many countries specify tolerance levels or population deviation limits from the electoral quota. The electoral quota is simply the population of the territory to be redistricted divided by the number of legislative seats (or districts) allocated to that territory.
Although the representation of voters has taken precedence over the representation of communities in the twentieth century--as evidenced by the number of countries that require districts to be as equal in population as possible--respect for administrative areas, physically-defined natural communities and geographically concentrated communities of interest continue to play prominent roles in redistricting. In fact, a primary function of single-member districts is to provide representation for geographically-defined communities.
Criteria Relating to Election Outcomes
Equal population, geographic considerations and communities of interest are criteria that relate directly to the process of creating districts. Other criteria relate to the outcome of the redistricting process--for example, requiring that district plans be drawn so that political parties are fairly represented or that racial, ethnic, religious or linguistic minorities have an equitable chance of representation. But countries that delimit districts usually do not adopt criteria relating to the fairness of the outcome. This is because countries with single-member districts can rarely meet these standards, if fairness of outcome is defined as proportional or near proportional representation for political parties and minority groups.
Conclusion
Redistricting criteria can conflict with one another. For instance, although almost all countries list population equality as a redistricting criterion, few countries actually have districts that are close to equal in population. The reason is that other criteria have been deemed more important than strict adherence to population equality. Respect for administrative boundaries and natural communities, for example, often require districts to be smaller or larger than the electoral quota.
Countries that establish redistricting criteria must either prioritise the criteria or accept certain inconsistencies in district configuration. Many countries choose to specify the most important criteria and/or place limits (such as population tolerance levels) on the redistricters, but still permit redistricters some discretion in balancing these criteria.
