GeoWorld July 2012

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Narrowing-In on Absurd Gerrymanders BEYONDMAPPING I BY JOSEPH BERRY Its bent-barbell shape is the poster-child of "stacked" gerrymandering, but Georgia's flying pig, Louisiana's stacked scorpions and North Carolina's praying mantis districts have equally bizarre boundaries. Coupled with census and party-affiliation data, n light of the current political circus, I thought a bit of reflection is in order on how GIS has impacted the geographic stage for the spectacle—literally drawing lines in the sand. Since the 1990 census, GIS has been used extensively to "re- district" electoral territories in light of population changes, thereby fueling the decennial turf wars between Democrats and Republicans. Redistricting involves redrawing of U.S. congressional-district boundaries every 10 years in response to population changes. In developing the subdivisions, four major considerations come into play: 1. Equalizing the population of districts. 2. Keeping existing political units and communities within a single district. 3. Creating geographically compact, contiguous districts. 4. Avoiding the drafting of boundaries that create partisan advantage or incumbent protection. Gerrymandering, however, is the deliberate manipulation of political boundaries for electoral advantage with minimal regard for the last three guidelines. The goal of both sides is to draw district boundaries that achieve the most political gain. Three strategies are applied: 1. Attempt to concentrate the voting power of the opposition into just a few districts, to dilute the power of the opposition party outside of those districts ("excess vote"). 2. Diffuse the voting power of the opposition across many districts, preventing it from having a majority vote in as many districts as possible ("wasted vote"). Joseph Berry is a principal in Berry & Associates, consultants in GIS technology. He can be reached via e-mail at 10 3. Link distant areas into specific, party-in-power districts forming spindly tentacles and ameba-line pseudopods ("stacked"). Fighting the Flying Pig, Stacked Scorpions and Praying Mantis For example, the 4th Congressional District of Illinois is one of the most strangely drawn and gerrymandered congressional districts in the country (see Figure 1). GEO W ORLD / JU L Y 2O12 GIS routinely is used to gerrymander congressional districts. But from another perspective, it can be used to assess a district's shape and, through legislative regulation, could impose indices that encourage com- pactness. A Convexity Index (CI) and a Narrowness Index (NI) are a couple possibilities that could be used to rein-in bizarre gerrymanders. Achieving Regularity and Cutting Cords The boundary configuration of any feature can be identified as the ratio of its perimeter to its area (see "Author's Notes 1 and 2," page 11). In planimetric space, the circle has the least amount of perimeter per unit area. Any other shape has more perimeter (see Figure 2), and as a result, a different CI. In the few GIS software packages having this capability, the index uses a "fudge factor" (k) to account for mixed units (e.g., m for P and m2 for A) to produce a normalized range of values from 1 (very irregularly shaped) to 100 (very regularly shaped). A theoretical index of zero indicates an infinitely large perimeter around an infinitesimally small area (e.g., a line without perimeter or area—just length). At the other end, an index of 100 is interpreted as being 100 percent similar to a perfect circle. Values in between define a continuum of boundary regularity that could be used to identify a cutoff of minimal irregularity that would be allowed in redistricting. Another metric for assessing shape involves calculating "narrowness" within a map feature. Figure 1. Examples of gerrymandered congressional districts show minimal compactness.

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