The Supreme Court recently issued an opinion on Perry v. Perez which seems like it must have involved evidence based on spatial analysis. The L.A. Times reports:

The 9-0 decision set aside a new map of congressional districts drawn by a special federal court in San Antonio that gave Latinos and Democrats a good chance to win three or possibly four new seats in the House of Representatives.

Does anyone know what type of spatial analysis - if any - was used to create the evidence presented?

Update: Thanks to mkennedy for interpreting this, and also for pointing me in the direction of preclearance. I see that the Federal Register Vol 76 No. 27 Part III goes into what I was wondering about under the "Retrogressive Effects". Fortunately, this is very googleable.

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    It wouldn't be the Supreme Court doing the analysis, per se. I'm sure that both the prosecution and defense contracted GIS professionals to conduct analyses, both trying to prove their own point. All the Supreme Court would do is essentially decide which party's analysis drew the more valid conclusions. – nmpeterson Jan 23 '12 at 18:29
  • @nmpeterson Thanks for the feedback, I've changed the question, does this make more sense? – Kirk Kuykendall Jan 23 '12 at 18:47
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    I don't know about the specific case in Texas, but geometric algorithms have been suggested as a way to quantify the degree of gerrymandering. Wikipedia describes a few, including one that computes the ratio of the area of the district to the area of the convex hull of the district. – dmahr Jan 23 '12 at 18:56
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    There is also a very interesting whitepaper on developing a gerrymandering index. "Congressional districts are indeed less compact now than they were ten years ago." – canisrufus Jan 23 '12 at 22:24
  • @dmahr Thanks, looks like compliance with Voting Rights Act would in some cases require strange geometries. – Kirk Kuykendall Jan 23 '12 at 23:32

Disclaimer: I'm definitely not a lawyer. The opinion is here. From skimming through it, it appears to me that the special federal court jumped the gun in producing a new map. The state's version hadn't been 'precleared' yet, but that map did not obviously violate any laws. It can still be challenged in court, but "in ordinary course." That is, a redistricting map was not needed in the short term for the upcoming elections. The existing map from the state can be used, even if it's undergoing a challenge.

Long and short: no spatial analysis was done. The decision was based solely on current laws and previous cases.

If I understand correctly, when a court needs expertise, they appoint a 'special master.'

  • Thanks for replying, I wish they'd express their opinions in language as clear as yours (jump the gun). Perhaps the bigger question is: what spatial analyses are performed in the preclearance process? – Kirk Kuykendall Jan 23 '12 at 23:07

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