Although many countries are considering the adoption of GIS software for redistricting, and a few are very close to being able to use this software in an upcoming round of redistricting (Australia and Canada, for example, are well on their way to developing GIS capabilities for redistribution purposes), very few countries to date have actually used GIS software specifically for redistricting. New Zealand is an example of one country that employed GIS software for their last redistribution in 1998. The country with the longest experience using GIS software for redistricting purposes, however, is the United States.
Although the number of states in the United States that were employing computers for redistricting purposes had been steadily growing since 1970, two important changes led to the dramatic increase in the number of states that used computers for redistricting during the 1990s:
- the diffusion of affordable GIS software.
- the introduction of a new computer database by the U.S. Census Bureau in 1990.
Prior to 1990, most states used a low-tech approach to redistricting: staff and legislators, in stocking feet, used grease pencils to mark proposed district lines on acetate overlays over large census maps spread out on the floor. Adding machines or handheld calculators were used to aggregate the population counts of the census areas that were being combined to create proposed districts. If computers were used at all, they were used as giant adding machines.
By the 1990s round of redistricting, however, every state in the United States used computers for redistricting, and almost every state used GIS software for redistricting. The major reasons for this shift was the increasing availability of GIS software, some explicitly designed for redistricting purposes, and the advent of a computerised map base of the entire nation by the U.S. Census Bureau.
In the United States, the U.S. Census Bureau is required to conduct an enumeration of the population every ten years and to supply the states with this population data for redistricting purposes. States, as well as local entities such as counties and cities, are required to redraw legislative lines on the basis of this data prior to the first election after the census.
The redistricting data produced by the Census Bureau is referred to as PL 94-171 data. It includes population counts for several different levels of census geography - units as large as whole counties, and units as small as census blocks (usually the equivalent of one city block), are reported in PL 94-171. Although the Census Bureau collects data on a large number of population characteristics, only a few items are included in the data files sent to the states for redistricting. These items are total population, voting age population, and subtotals of the population for persons of Hispanic origin and for five major racial groups: white; black; Asian and Pacific Islander; American Indian, Eskimo, and Aleut; and 'other' races. This data has been available in electronic format since the 1980 round of redistricting.
In addition to population counts of the entire country, the Census Bureau also maintained a master set of 26,000 maps of varying sizes and scales of the country. These maps were drawn by hand, and were often difficult to read and filled with errors. In preparation for the 1990 census, however, the Census Bureau created a computerised database of the entire country called TIGER (Topographically Integrated Geographic Encoding and Referencing). The TIGER database depicts visible geographic features such as roads, rivers, and railroads; a whole hierarchy of census geographic units (for example, census blocks, block groups, and census tracts) for the collection and reporting of population data; the boundaries of administrative subdivisions such as counties, cities and towns; and political geography such as congressional districts and, in some cases, voting areas - referred to as election precincts in the United States. Maps produced from the TIGER database provided U.S. redistricters with uniform, digitised maps for the entire country for redistricting purposes in the 1990s.
As the TIGER files became available, GIS software was also increasing in availability. A number of commercial companies offered GIS software that was customised specifically for redistricting purposes, in fact. These GIS software packages were able to relate information on population demographics, taken from the census, and political data from previous elections to the computerised TIGER base maps showing geographic census units, election precincts, street networks, natural and built landscapes, other jurisdictions boundaries, and other geographic features.
The implications of these new products was overwhelming for those involved in redistricting: affordable GIS software and a consistent nation-wide computerised database that included both census data and digitised maps was available for both those charged with the task of redistricting and for those simply interested in evaluating proposed plans and producing alternative plans.
One of the substantive results of this confluence of events was the active and informed participation of numerous interest groups that had previously been excluded from the redistricting process in the United States. The participation of civil rights groups, in particular, led to the adoption of redistricting plans in many states that gave minority groups much greater representation in the halls of government. For example, 24 new minority congressional districts - districts in which minority voters made up a majority of the voters - were created and more minorities elected to Congress than ever before. To create these districts within the tight population equality constraints imposed, however, a number of other districting values had to be compromised - in particular, the geographic compactness of these districts.
This case study illustrates some important points to be made about the use of GIS software for redistricting.
- The availability of electronic data and computerised maps makes the adoption of GIS software for redistricting a relatively simple task. Because the U.S. government provided the electronic data and computerised maps for the entire country - and at a very low price - redistricters were able to make use of GIS software without having to be concerned with creating an electronic database.
- Many public interest groups were also able to purchase the electronic data and GIS software because of the affordable price. These groups used the data and software to evaluate proposed redistricting plans and to create alternative plans. This information was used to hold the redistricters accountable and certainly had a democratising influence on the process in many instances. (Clearly, the increase in the number of minority districts drawn during the 1990s round of redistricting is directly attributable to the active monitoring of the process by minority and civil rights groups.)
Although there is potential for GIS software to 'democratise' the redistricting process, this is possible only if the boundary authority is truly non-partisan or if all parties and interest groups interested in the redistricting process can gain access to the necessary data and technology. As computers and GIS software become more affordable, this is becoming less of a problem. But in many countries, the necessary hardware and software may still be prohibitively expensive to most groups. In addition, training on the use of GIS may be difficult to acquire.
