Welcome, Guest. Please login or register.
Did you miss your activation email?
December 10, 2017, 07:16:04 pm
HomePredMockPollEVCalcAFEWIKIHelpLogin Register
News: Be sure to enable your "Ultimate Profile" for even more goodies on your profile page!

+  Atlas Forum
|-+  General Politics
| |-+  Political Geography & Demographics (Moderator: muon2)
| | |-+  US House Redistricting: Tennessee
« previous next »
Pages: 1 2 3 4 5 6 [7] Print
Author Topic: US House Redistricting: Tennessee  (Read 22472 times)
Torie
Moderators
YaBB God
*****
Posts: 35873
Samoa


View Profile
« Reply #150 on: January 09, 2013, 10:55:08 am »
Ignore

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?

« Last Edit: January 09, 2013, 11:28:58 am by Torie »Logged
muon2
Moderator
YaBB God
*****
Posts: 13142


View Profile
« Reply #151 on: January 10, 2013, 12:19:59 am »

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?

It is certainly true that I could set up the same measures directly to the district level. In that case the regions would serve to guide the mapper towards possible county groupings that would likely do well in the final scoring. That's actually the way I used them when I drew my OH maps that did well in competition, since there was no score or knowledge of my intermediate steps.

If one does require a Pareto optimization of regions as well as districts it provides a constraint on the mapper that should tend to force better connected groups of counties together. That's a plus for improving maps where connectedness is presumed to relate to communities of interest.

It is also the case that the computerization of redistricting remains hard, and for the number precincts (far worse for census blocks) the problem is sufficiently hard that the best maps would be difficult to draw in reasonable times. By splitting the problem into two tiers - one for regions and one for districts, the computational problem becomes exponentially easier. This also implies that human mappers would have to focus on a reduced set of options providing a key constraint against hidden gerrymandering.

Quote
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!

For the four states I've done (WI, WV, WA and TN) I used a paper atlas, Mapquest, and Paint to create the links. It takes a couple of hours. It's easy to visually count the cuts once I g=have a map, but it would also be straightforward to put the links in a table and have a simple program measure the plan. One could make a blank county map and have users color code them just like election prediction calculators do for region construction.

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



I presume that real splits would use data at a finer level than precincts. That's certainly needed to avoid chopping cities when precincts overlap the boundaries. States generally redraw precincts after a remap causes splits anyway.


But let me assume that for municipal split purposes you really want a district boundary to follow the image above. If 70S continues along the boundary to the west and eventually to the population center for the blue piece of the county then there is a link between the blue part of the west county and the east county. That link would count for erosity.

In your Nashville plan, there is no link from north Davidson (CD 5) to Rutherford county (CD 6) north of the lake, leaving only south Davidson linked to Rutherford, but that's an internal link not counting for erosity. However, as you drew it there are links from both north and south Davisdson to Cheatham county so that increases the erosity by one more than would otherwise exist on the border of those counties.


In my tweak to your plan I shift the boundary south of I-40 so there is no link from south Davidson to Cheatham, but south Davidson remains well connected internally along 100.
Logged



Great American Eclipse seconds before totality showing Baily's Beads.
Torie
Moderators
YaBB God
*****
Posts: 35873
Samoa


View Profile
« Reply #152 on: January 10, 2013, 11:36:51 am »
Ignore

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.
Logged
muon2
Moderator
YaBB God
*****
Posts: 13142


View Profile
« Reply #153 on: January 11, 2013, 11:33:01 am »

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.

My general rule is that when a county is chopped, each chop part now acts as a new county for the purpose of connections and thence erosity. Connections between counties depend on a path of numbered federal and state highways between population nodes. The population node is determined by the largest urbanized area (census maps) or the county seat if there is no urbanized area, or the largest population incorporated or census designated place if none of the other choices are available. Within an urban area the largest population within the county is used for the node. This can be either incorporated or unincorporated, or the downtown within a large city (typically including city hall).

It's easier to start with examples from eastern TN. This is my split of Grainger. There are no urbanized areas in Grainger so county sear Rutledge is the population node. It stays in the northern chop and Blaine is the largest place in the southern chop, so it is the population node for determining connections.

Grainger (Rutledge) is connected by state or federal highways to to Claiborne, Hancock, Hawkins, Hamblen, Jefferson, Knox, and Union. The split of the southern part around Blaine is only connected to Knox, and the remaining northern part is connected to the remaining counties, but not Knox. This is an ideal chop that has no increase in erosity.



This is my split of Blount. Much of the population of the county is within the Knoxville urban area which doesn't show on the DRA map. Maryville is the largest place and within that urban area and is the population node for the county which is connected to Monroe, Loudon, Knox, and Sevier. The northern part including Maryville is only connected to Knox and Sevier.

The southern part has the largest population in the urban area in unincorporated Binfield, and the largest place is the much smaller Friendsville. Binfield has the larger population in the urban area and is used as the node connecting to Monroe and Loudon. Friendsville only links to Loudon, but a connection that exists at the county level cannot vanish by the means of a district line, so the Monroe connection would have to remain there as well. This chop also separates the county connection in a way that does not increase their number.



Davidson county is problematic to define since Nashville includes all of the county not in the few small communities. The northern part has the downtown so that defines its node. The southern part has more population in Nashville than in the smaller separate cities and the largest part is along I-24 so that defines the node for connections.

Davidison connects to Cheatham at the county level, but doesn't need to have connections to both the northern and southern chops of Davidson depending on where the line is drawn. By following the river at the Cheatham line you provide a connection to the south Davidson node along TN-1, TN-100 and TN-254. By moving the line south as I do I remove the link from Cheatham to south Davidson. If I had controls I'd make my cut more cleanly than the course VTDs in DRA.

Yes, it may seem arbitrary that our two plans seem reasonably equal by eye in Nashville, yet differ by this measure. The difference is that without my constraint on erosity, a mapper is free to place the line at Cheatham anywhere they want and that opens the door just a bit to gerrymandering. The idea is that a reasonable set of constraints can limit gerrymandering yet provide flexibility.
Logged



Great American Eclipse seconds before totality showing Baily's Beads.
Pages: 1 2 3 4 5 6 [7] Print 
« previous next »
Jump to:  


Login with username, password and session length

Logout

Powered by SMF 1.1.21 | SMF © 2015, Simple Machines