Computers can be extremely useful in the delimitation process9. They can reduce the time required to draw redistricting plans and also aid in the evaluation of plans. They can produce detailed maps and statistics based on the demographic and political information in the redistricting database. And because computers allow redistricters to create plans more quickly, they enable redistricters to generate a larger number of redistricting plan alternatives for comparison and evaluation.
In the United States, about half the states used computers when congressional districts were redrawn after the 1980 census. In most of these states, computers were used as 'super calculators' to summarise demographic and political data and to produce printouts of demographic information for the proposed districts.
Two important developments in the late 1980s contributed to a far greater use of computers for redistricting in the 1990s. These were (1) the development and the extensive use of powerful, affordable desktop computers and (2) the development of geographic information systems (GIS) software. GIS software is an integrated system for displaying demographic data on a computerised map.
In 1990, every state in the United States used computers for redistricting, and almost every state used GIS software. The move towards computer-assisted redistricting was also aided by the availability of detailed demographic and geographic data in computer readable formats from the U.S. Census Bureau.
Desktop Computers
Today, a Pentium desktop computer has as much, or more, computing power than many of the expensive mainframe computers used in the 1980s. And a Pentium desktop computer is affordable. In addition, there are now a variety of inexpensive devices for printing maps.
Computer Software
Redistricters have several different options from which to choose with regard to software. A simple spreadsheet or database program can calculate the statistics that are commonly used in redistricting, such as total population, racial composition or overall population deviation from the electoral quota. Several software vendors in the United States offer database or spreadsheet programs specifically adapted for redistricting. A more sophisticated and more expensive option is GIS software.
GIS Software
There are GIS software packages available that are specifically tailored for redistricting. GIS redistricting software provides redistricters with the following capabilities:
- draw district plans interactively by assigning geography to districts piece by piece and seeing the results displayed on the computer immediately;
- produce maps, both on the computer screen and in printed form;
- generate statistical reports for the redistricting plan and each individual district in a plan.
Redistricters using GIS software have a variety of sophisticated tools at their disposal for creating district plans. GIS software can be used to draw new districts by assigning geographic units to districts or by moving particular geographic units out of one district and into another. The effects of the reassignment on the population, or any other demographic or political characteristics of the districts, can be immediately reflected on the computer screen. Once a new plan has been created, the GIS software, with the aid of a laser printer or plotter, can produce a map of the new district plan or any individual district. GIS software essentially consolidates all redistricting operations into one efficient system.
Examples of the kinds of maps and reports that can be produced with GIS software can be found in GIS redistricting software output. Computer screen maps of an entire redistricting plan and a zoom-in on one section of the plan have been printed out and are included, as well as a population report and a political report detailing information about each district and the plan as a whole. The GIS software package that produced these items was customised and distributed by an American consulting firm, Election Data Services, Inc., for use during the 1990s round of redistricting in the United States.
The resources necessary to employ computer technology for redistricting include:
- a computer (desktop or mainframe)
- spreadsheet or database software, or GIS software
- population and, if desired, political data available in electronic form (if only paper copies of the information are available, the data will have to be keypunched into the computer program)
- maps (either paper maps or digitised maps if GIS software is to be used)
