US House Redistricting: Tennessee

[Torie]

Just for kicks, I did a Pub gerrymander light for TN, which creates a nice competitive CD for the TN-05, which should make the AZ "non-partisan" redistricting commission proud. Its underlying leitmotif is that it keeps the black community of Nashville together (a few inner white liberal precincts are excised in partial exchange), and does but one split of Davidson County. It also makes sense in other ways I think, with the Nashville metro area divided between 2 CD's.

[Torie]

Oh Muon2 your map above might work as a Pub gerry-lite, but I must say my tweaked map below appears to me to be superior to your algorithmic map. TN-5 is 50.0% McCain, 48.8% Obama, and TN-06 is 57.3% McCain, 41.6% Obama.



Your cut of Davidson appears to slice the black community by the way. I assiduously avoided that in my map (the NW black node is entirely in TN-05, albeit a handful of substantial black minority precincts in the geographically separated by white precincts SE node are in TN-06). And notice how it keeps downtown Nashville whole, and uses that lake as a barrier on the east side. Natural barriers are there to be used where possible - not ignored.




What do you think?  I am still a little confused btw what the real purpose of the regional overlay is in your formula, above and beyond county cut containment. Is to to take cognizance of metro areas, and keeping them whole, ultimately, or is there more? Is it a way to contain erosity, or limit erosity to where it ties together "regional" communities of interest?  In any event, everyone "knows" the regions of Tennessee, including most of its citizens, and my map took that into account. I like there being one middle TN rural CD, TN-04 (with rural TN-07 being 75% Middle TN, and 25% West TN by necessity to equalize population), and two CD's that cover the Nashville metro region, and no more, and fit like a glove over that metro area. That is how it should be.  I also tried to limit just visual erosity, and move towards rectangular squarish shapes. And I looked at road ties in East TN, and moved stuff around a bit accordingly, including moving Sevier County into the Knoxville CD, where it properly belongs really, rather than TN-01.

[Torie]

Muon2, how did you define regions for TN (population driven, or historically driven, or both?), and the road splits only count when a CD splits a region?  I still don't quite get the mechanical aspect of regions in your methodology.

[Torie]

Muon2, how did you define regions for TN (population driven, or historically driven, or both?), and the road splits only count when a CD splits a region?  I still don't quite get the mechanical aspect of regions in your methodology.

A region is a connected set of counties that has a population nearly equal to a whole number of districts. The use of roads determines connectedness, and the severed connections also serve to measure erosity. When a county is split within a region then each piece is treated as if it were a separate county for connections and erosity.

The main idea is to recognize that split counties (or cities) and erosity both point at potential gerrymandering and generally point away from maintaining communities of interest. My goal is to create a mechanism whereby those two factors can be balanced against each other and balanced against population equality.

That statement suggests regions serve no purpose whatsoever, unless road splits that hew to regional lines don't count, or regional lines must be followed except to round up or down to whole CD's in the case of the one CD that will cross regional lines. It seems more a matter of convenience in calculating where CD's will end up going. And what is to prevent erose regions, if regions are strictly driven by population?

How did you map out all those roads by the way on the computer, and then efficiently count the splits btw?  That seems like a heck of a lot of work!

By the way, does the inconveniently shaped precinct below jutting across a highway effect an additional road split?

[Torie]

Yes, there is no road split between Cheatham and South Davidson, but one more road split between North Davidson and Cheatham, so why one less road split with your revision of my map?
 I am confused again. In all events, as an factual matter, there really is no greater erosity or lack of connectedness, but until I understand your program clearly, there is no point going there.