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 criteria.
Criteria Related to Geographic Boundaries
Respect for clearly established boundary lines is often specified as a criterion for those redistricting to consider when drawing electoral district lines. These boundaries can include administrative boundaries such as county and municipality lines and/or natural boundaries created by dominant topographical features such as mountain ranges, rivers or islands.
Geographic redistricting criteria such as respect for administrative boundaries and physically defined natural communities are a higher priority in some countries than in others. In the United Kingdom, for example, respect for local administrative boundaries and natural communities is the most important concept guiding boundary commissioners. Large population disparities are tolerated as a result.
Criteria Related to Geographic Size and Shape
Factors such as the remoteness of a territory, the sparseness of population, or geographic accessibility are sometimes listed as criteria to consider when drawing district lines. 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.
Two other factors that are sometimes listed as redistricting criteria relate specifically to the geometric shape of a district--contiguity and compactness. Advocates of these criteria hold that districts should not be oddly shaped and that all pieces of a district should be inter-connected. The latter criterion seems to have been taken for granted by redistricting authorities almost everywhere and is specifically mentioned as a rule in a number of countries. For example, many state constitutions in the United States list contiguity as a requirement for legislative districts. Recently, this issue has led to disagreements in some states in the United States as to whether a district connected by a single point is, in fact, contiguous.
The issue of district compactness, like contiguity, is often taken for granted and may or may not be specifically listed as a criterion to consider. When it is listed, compactness is rarely defined. Like contiguity, the issue of compactness has led to disagreements, and even court challenges, in a number of states in the United States. The U.S. Supreme Court has recently ordered the redrawing of a number of oddly shaped 'majority minority' congressional districts. Although the shape of these districts was not the basis for the Court's decision, the fact that the districts were not compact was considered evidence of an impermissible motive in creating the district boundaries. (For additional discussion of these court cases see Role of the Courts in Electoral District Delimitation.)
