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COMPUTING SCIENCE

Machine Politics

Brian Hayes

Point-and-Click Redistricting

The computer is already an essential tool in redistricting; no state today draws its districts with Magic Markers. The computer tools in common use are interactive programs. You sit at a display screen showing a state map that can zoom in on individual counties, precincts or census tracts. You select a geographic unit on the screen and then issue a command to assign it to a district or transfer it from one district to another. The system offers immediate feedback on the political and demographic consequences of each move. You see at a glance the population of each district, its racial and ethnic composition and various indicators of political allegiance.

Underlying this interactive facility is a database linked to the map. Basic demographic data come from the Census Bureau, with populations broken down into geographic units as small as the census block, which generally comprises about a dozen houses. Political intelligence-such as numbers of registered voters, party affiliations, voter turnout statistics and the results of key elections-has to be collected from county boards of elections. The hardest part of building the database is reconciling data from different sources. Boundaries of wards and precincts don't necessarily coincide with the boundaries of census blocks, and so interpolation is needed. (For the 2000 census, the states and the Census Bureau are cooperating to make the boundaries more consistent, which means the next census should be a more efficient tool for the gerrymanderer.)

The introduction of computers into the redistricting process has allowed more precise analysis of proposed plans. A map can be fine-tuned by shifting individual census blocks from one district to another, whether to equalize populations or to achieve political goals. It is no accident that in many states both major parties have access to their own computer systems for redistricting.

For the 1990 round of redistricting most states employed proprietary software specially designed for the purpose and running on mainframes or minicomputers. For the 2000 round there is growing interest in adapting more versatile geographic information systems to redistricting, and running them on client-server networks of computers. But these systems too are mere interactive aids to the human redistricter; they do not make autonomous decisions about where to draw boundary lines.





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