Many countries have instituted a set of formal rules, or criteria, for their boundary authorities to consider when drawing electoral districts. These redistricting criteria often include stipulations 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 means of transportation and/or communication as well. All of these criteria relate directly to the process of creating districts.
Another set of possible redistricting 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.
Regardless of whether the criteria relate to the process or the possible outcome, geographical information systems (GIS) software can often be used to measure compliance with these criteria.
Equal population
The most widely accepted rule for redistricting is that districts should be relatively equal in population. This is because representation by population is a central tenet of democracy and, in countries that employ single-member districts, this rule translates into the principle of equal populations across districts. Districts that are equal in population are necessary if voters are to have an equally weighted voice in the election of representatives. If, for example, a representative is elected from a district that has twice as many voters as another district, voters in the larger district will have half as much influence as voters in the smaller district.
The degree to which countries demand population equality varies. The United States is unique in its adherence to the doctrine of equal population. No other country requires deviations as minimal as the "one person, one vote" standard that has been imposed by U.S. courts since the early 1960s. New Zealand comes closest to that strict standard, with deviations of five percent or less from the electoral quota permitted.
Other countries, while recognising the importance of population equality, have chosen to balance this factor against other redistricting criteria perceived as equally valid. In the United Kingdom, for example, respect for local administrative boundaries is given precedence over exact equality of number. In many African countries, the need to recognise individual tribes may take precedence over population equality. Each country must determine how much variation from the ideal of exact population equality will be tolerated to accommodate other redistricting goals.
Summary reports listing the total population of each district in a redistricting plan is necessary to determine whether a particular plan meets the criterion of equal population, regardless of what level of adherence is required. If GIS software has been used to create the plan, a statistical report listing the population of each district, as well as the percent that district deviates from the population quota, is a very simple matter. An easyclick of the mouse will produce the needed report.
Geographic considerations
In many countries, the electoral laws specify that geography, or certain geographic factors, be taken into account when delimiting electoral district lines. Geographic criteria can be divided into two categories: criteria relating to geographic boundaries and criteria relating to geographic size and/or shape. A boundary authority may be asked to consider factors from either or both categories.
With regard to criteria related to geographic boundaries, for instance, a redistricting authority may be required to respect administrative boundaries such as county and municipality lines and/or natural boundaries created by dominant topographical features such as mountain ranges, rivers or islands. Factors such as the remoteness of a territory, the sparseness of population, or geographic accessibility are common examples of criteria related to geographic size. These factors are particularly important in countries which have large, sparsely populated territories, like Canada, Australia or Russia, or countries with islands or other isolated constituencies that are more difficult to serve. In addition, some countries require redistricters to take into account factors, such as whether the districts are geographically compact.
GIS software enables redistricters to produce maps of the newly created districts instantaneously. These maps allow redistricters to view the configurations of the newly created districts and to overlay administrative, political and natural boundaries onto the new district plan in order to access the degree to which these boundaries coincide with the new district lines. Often, not only is the map of the new districts instantly available, but statistics relating to the size and even the shape of the districts can be calculated and instantly reported. For example, some GIS packages can display the length or perimeter of a district in miles or kilometres as well as mathematical measures of geographical compactness.
Communities of interest
Because electoral districts are usually required to be relatively equal in population, single-member districts often do not reflect distinct geographic communities as signified by municipal, county or other administrative divisions. This does not mean, however, that political representation has been divorced from the notion of "community" in countries that redistrict—many countries that delimit single-member districts continue to emphasise the importance of creating districts that correspond as closely as possible to pre-existing communities, defined as administrative divisions and/or "communities of interest."
The rationale for recognising communities in redistricting is that electoral districts should be more than conglomerations of arbitrary, random groups of individuals. Districts should, as much as possible, be cohesive units with common interests related to representation. These shared interests may be the result of a common history or culture, a common ethnic background, or a variety of other ties that create a community of voters with distinct interests.
GIS software can be used to ensure that previously identified communities of interest are respected if the boundaries for these communities have been digitised and inserted into the redistricting database as a boundary layer. This may be a relatively simple task if communities of interest are taken to be administrative subdivisions, for example, or other regional or local communities that have well-established boundaries. This is more complicated, however, if the boundaries are not clearly defined.
Fairness for political parties and minority groups
Criteria specifying fairness for political parties and minority groups within a country focus on the electoral outcome, rather than the process, of redistricting. Electoral systems that rely exclusively on single-member districts, however, cannot guarantee proportional representation or even some minimal percentage of seats for minority political parties or for ethnic, racial, linguistic or religious minority groups in the population. This is because single-member districts inevitably produce disproportionately fewer seats for minority parties and minority groups, unless these groups are geographically concentrated in such a way that line drawers can create a proportionate number of districts in which these groups predominate, or special electoral provisions have been made to ensure certain minority groups some representation in the legislature.
Another approach to dealing with the inherent disproportionality of single-member districts is to adopt redistricting reforms designed to ensure a fair and impartial redistricting process. Reforms such as the adoption of independent, non-partisan commissions and neutral redistricting criteria do little to alleviate disproportional election outcomes, however. Taking the politics out of redistricting does not mean that a districting plan has no political effect—it simply guarantees that any political bias in a districting plan is unintentional.
Still another means of dealing with the potential political impact of a redistricting plan—and perhaps the most practical approach—is to attempt to determine the likely political implications of a proposed redistricting plan prior to enacting the plan. If political data (previous election results) have been included in the redistricting database, GIS software can use this information to make predictions regarding the likely political impact of a proposed redistricting plan. GIS software can do this by recompiling previous election results to conform with the newly proposed district lines.
Of course, simply being able to predict the likely political impact of a redistricting plan is not enough to ensure that a plan that is as fair as possible to all political groups will be adopted. Only if the redistricting authority is truly non-partisan or if all interested groups and citizens are armed with this information—and can therefore hold the redistricters accountable—can this approach succeed.
If a redistricting authority has a specific political agenda, sole access to this kind of information and/or sole discretion as to what plan to adopt, this information can actually result in a politically biased plan. This may be the reason that many redistricting authorities are not permitted to consider any political data at all when drawing district lines. However, it should be noted that political parties often have access to this kind of information, even if the redistricters do not, and may use this information to influence the boundary authority during the public hearing process. This is one example of why it is important to consider the context under which redistricting plans will be promulgated in deciding whether to use GIS or not.
