[EM] Re: Automated districting

Adam Tarr atarr at purdue.edu
Sun Jan 11 11:20:02 PST 2004

>>However, the only objective consideration in drawing census tracks that I 
>>am aware of (in the U.S.) is that they contain 5-10,000 persons, which 
>>leaves census tract drawing vulnerable to political manipulation.
>I think this number is actually the crux of the issue.   If the size of a 
>census tract is far smaller than the size of the district, then I would 
>argue it doesn't matter how much bias there is in how the tracts are 
>defined.  I think we can count on at least 10 tracts per district, as a 
>conservative assumption.

In the case of congressional districts, that's a VERY conservative 
assumption.  The average congressional district has over 600,000 people in 
it.  When you have that many census tracts, manipulation of the algorithm 
is simply impossible.

Consider, further, the nature of a gerrymandered district.  Gerrymandering 
typically produces long, sliver-shaped districts that try to capture a 
particular constituent.  But what to slivers have a lot of?  Perimeter 
length, that's what.  That means lots of road connectivity to the 
surrounding districts, which means it's pretty unlikely that they would be 
split apart by this algorithm.  Which means the gerrymandering tends to 
produce no effect.

>If someone was willing to precisely define the conditions, I could 
>probably code something up.

Well the first step would just be to write the basic algorithm: one that 
takes a weighted graph and returns the N subgraphs that results in the 
lowest total severed edge weight.  You would also need to assign a 
population number to each node, and require that the total solution have 
roughly equal population in each sub-graph.


More information about the Election-Methods mailing list