[EM] Re: Automated districting
Adam Tarr
atarr at purdue.edu
Fri Jan 9 09:19:01 PST 2004
We talked about districting here in the spring of 2002, and came to what
seemed to be a satisfying conclusion to me:
http://groups.yahoo.com/group/election-methods-list/message/9223
Thumbnail sketch of the proposed idea:
1) Treat the census blocks as "atoms" of the eventual districts, i.e. they
cannot be split up into two districts.
2) Form a graph of the states where the nodes are census blocks, and the
edges represent physically adjacent census blocks.
3) Weight each edge by the amount of road connectivity between the
adjacent bolocks. The simplest metric would be number of lanes of traffic
that fall on the dividing line. Basically, you want the edge weight to
represent how connected those two census blocks are in reality. Ideally,
what you'd want is a count of how many people cross the border per year,
but that's obviously unrealistic, so the road bandwidth is a good
approximation.
4) When you set up districts, you are essentially taking the large graph
of the entire state and dividing it into several small sub-graphs which
each represent a district. To do so, you cut every census block-to-census
block edge along the district boundary.
5) THE AUTOMATED ALGORITHM would take the weighted graph that represents
the entire state, and divide it up into the equal population solution THAT
MINIMIZES the total weight of the severed edges.
Such an algorithm may be difficult to write, but writing a program that
could iterate on an approximate solution could be pretty easily.
-Adam
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