Drawn Together: Can Math Nerds Beat Gerrymandering?
How to spot a gerrymandered congressional district.
By Dave Gilson | Tue Sep. 21, 2010 2:00 AM PDT
The art of drawing congressional districts to benefit one party or another goes back [2] to the earliest days of the
republic. Detailed census and election data have made it even easier to construct electorates with an all-butguaranteed political leaning. You can usually spot a gerrymandered district by its wacky boundaries. Or you can
use this formula [3](PDF), developed by John Mackenzie, a professor of resource economics and geographic
information systems at the University of Delaware:
G = gP/A
G: gerrymandering score
g: the district's boundary length, minus natural boundaries
(like coastlines and rivers)
P: the district's total perimeter
A: the district's area
Mackenzie's formula gives lower gerrymandering scores to
districts with a low perimeter-to-area ratio (like the entire state
of Wyoming [4]). Higher scores go to irregularly shaped
districts, like Illinois' pincer-like 4th district (right).
The formula doesn't take into account how a district got its odd contours. Take
North Carolina's 12th, which has the country's third-highest gerrymandering
score. Drawn as a majority-black district in 1992, the snaking "I-85 district [5]"
used to be barely wider than the interstate in some places. After being found
unconstitutional by the Supreme Court, it was redrawn in 1997 with a slight white
plurality. But it's kept [6] its meandering shape, and its representative—Rep. Mel
Watt, a black Democrat.
So what might an ungerrymandered nation look like? Mathematician Warren D.
Smith, cofounder of RangeVoting.org [7], has used an algorithm[8] to redraw
every state's districts in a geometrically precise manner that ignores party lines
(left). Would his solution shake up the partisan or racial composition of Congress? Who knows. But it sure
would look pretty.
Source URL: http://www.motherjones.com/politics/2010/09/gerrymandering-math
Links:
[1] http://motherjones.com/politics/2010/08/matt-angle-texas-redistricting
[2] http://sshl.ucsd.edu/gerrymander/
[3] http://www.udel.edu/johnmack/research/gerrymandering.pdf
[4] http://www.govtrack.us/congress/findyourreps.xpd?state=WY
[5] http://www.senate.leg.state.mn.us/departments/scr/redist/redsum/ncsum.htm
[6] http://www.watt.house.gov/index.cfm?sectionid=27&sectiontree=27
[7] http://www.rangevoting.org/
[8] http://www.rangevoting.org/GerryExamples.html