Fellow map nerds! I need a favor!

[Alcon]

I'm helping out with a major local presentation on redistricting.  One point they want to make is that maps that are totally geographically neutral, or exclusively encourage competitiveness, end up with pretty ridiculous-looking districts.  They want to show examples.

Do any of y'all have some free-for-use maps that show that?

1. A map that doesn't regard communities, keeping the most compact districts, and showing how ridiculously random those districts end up

2. A map that tries to create the most competitive possible districts, and ends up looking super gerrymandered.

State doesn't matter.

Thanks!

[muon2]

It depends on how extreme one wants to be. Let's consider compactness. There are 50 or more mathematical definitions of compactness.

For one that best ignores any sense of community there's the splitline algorithm. Compactness is defined by minimizes the line that splits the state's population into districts. It ignores everything except where the population lies within the state and goes for maximum compactness. Here's what they came up with for IA using the 2000 Census results.



Of course the actual approved IA map for that decade also followed pure geographic neutrality, but it defined compactness by minimizing the difference between the horizontal and vertical dimensions as well as the perimeter. However, it also keeps all counties whole, so it uses that as a proxy for community integrity.

[muon2]

Now let's look at maximum competitiveness.

Here's a map of OH I posted two months ago. All CDs are within 500 of the quota and no muni is chopped except for Columbus. There is a VRA district with 47.2% BVAP. All other districts had a plurality for Obama in 2008. The margin of victory ranges from 438 to 2824. It looks pretty well gerrymandered with 15 out of 16 competitive districts.



However, a plan that still preserves competitiveness in 11 out of 16 districts doesn't look as crazy. This was the Ohio redistricting competition winner in 2011 and it maintains a high degree of compactness and splits few counties. It also was designed to have an 8-8 delegation in a 50-50 election year.

[traininthedistance]

Seconding muon's suggestion of the splitline maps as a good example of Point 1.  Louisiana is one of the more ridiculous, especially with New Orleans split north-south with half of it connected to the other side of Lake Pontchartrain.  Obviously, most urban areas get shafted with splitline in such a manner, but the lake makes it particularly obvious.



And I'm not entirely sure, but that district might take in a tiny bend in the Mississippi up in the north of the state, too.  By sheer luck, they don't seem to do anything particularly egregious to the Eastern Shore of MD, which also would have been a great example.

[Simfan34]

Do you have maps of redistricting proposals that look sensible but are in fact rather skewed- to the Reps if there any?

[Alcon]

This is great -- thanks, all.

[jimrtex]

Seconding muon's suggestion of the splitline maps as a good example of Point 1.  Louisiana is one of the more ridiculous, especially with New Orleans split north-south with half of it connected to the other side of Lake Pontchartrain.  Obviously, most urban areas get shafted with splitline in such a manner, but the lake makes it particularly obvious.



And I'm not entirely sure, but that district might take in a tiny bend in the Mississippi up in the north of the state, too.  By sheer luck, they don't seem to do anything particularly egregious to the Eastern Shore of MD, which also would have been a great example.

Splitline is a recursive algorithm that divides an area in two (nearly) equal parts, by finding the shortest line that divides the area into two subareas of the correct population.

So the first cut in Louisiana divided the state (2000 population) 3:4, with the line just east of Lafayette and going into Mississippi between Angola and Natchez.   An indention such as that formed by Mississippi is greatly favored by Splitline since a short cut can be drawn at almost any angle.  The line doesn't nick the bend in the Mississippi, because if it did, it would have made the cut line from the Gulf Coast much longer.  Instead it just misses the bend so that the cut ends at the southern border of Mississippi.

A more north-south cutline would have to cut through Baton Rouge, plus the state is a bit thicker where the Atchafalaya discharges into the gulf.

The western part of the state is much longer in the north-south direction, so the division of a 3-district area is split on an east-west line in 1:2 parts, isolating the blue Lake Charles-Lafayette district.   The cut line takes advantage of the slight bulge of Texas south of Natchitoches and is almost perpendicular to the first cut line.

The final cut in the west is the north south split between the Shreveport-Natchitoches and Monroe-Alexandria districts.  There must be enough population in the northern part of this area (Shreveport and Monroes) that would force the cut so far north that it would be where the state widens out as it goes north.

The eastern 2:2 split takes advantage of the bay just to the west of the birdfoot delta, and avoids nicking Grande Isle.  It also picks up just enough of the western suburbs of New Orleans to make equal shares of the population.

[jimrtex]

Now let's look at maximum competitiveness.

Here's a map of OH I posted two months ago. All CDs are within 500 of the quota and no muni is chopped except for Columbus. There is a VRA district with 47.2% BVAP. All other districts had a plurality for Obama in 2008. The margin of victory ranges from 438 to 2824. It looks pretty well gerrymandered with 15 out of 16 competitive districts.



However, a plan that still preserves competitiveness in 11 out of 16 districts doesn't look as crazy. This was the Ohio redistricting competition winner in 2011 and it maintains a high degree of compactness and splits few counties. It also was designed to have an 8-8 delegation in a 50-50 election year.

I've seen a map that the proponents of the 2005 Ohio redistricting proposition had prepared.  It placed extreme emphasis on competitiveness and whole counties, and had districting radiating outward from the northeast, with Lorain, Medina, Summit, Geauga, and Lake in different districts to reach out to pick up Republican voters.  It would be a good example.

[traininthedistance]

An indention such as that formed by Mississippi is greatly favored by Splitline since a short cut can be drawn at almost any angle.  The line doesn't nick the bend in the Mississippi, because if it did, it would have made the cut line from the Gulf Coast much longer.  Instead it just misses the bend so that the cut ends at the southern border of Mississippi.

Aha, I see. Thanks for the explanation.

[memphis]

Do you have maps of redistricting proposals that look sensible but are in fact rather skewed- to the Reps if there any?

This is the actual Michigan House map.

[Sprouts Farmers Market ✘]

I was actually going to post that Michigan one too because of MI-01. I actually think it used to be gerrymandered going down to Bay County on the eastern sidea which is far more Democratic. I think it's much more sensible as is now despite giving the Republicans an overwhelming majority. When the most sensible looking district is the only swing dustrict, you know the rest is natural. Sure, there are some odd shapes down south but they are really just changing it from pvi +30 to pvi +25. At that point, let the people get a congressman from their own party. The primary is effectively the election.

[Sol]

I was actually going to post that Michigan one too because of MI-01. I actually think it used to be gerrymandered going down to Bay County on the eastern sidea which is far more Democratic. I think it's much more sensible as is now despite giving the Republicans an overwhelming majority. When the most sensible looking district is the only swing dustrict, you know the rest is natural. Sure, there are some odd shapes down south but they are really just changing it from pvi +30 to pvi +25. At that point, let the people get a congressman from their own party. The primary is effectively the election.

How on earth is splitting Lansing fair?

[traininthedistance]

I was actually going to post that Michigan one too because of MI-01. I actually think it used to be gerrymandered going down to Bay County on the eastern sidea which is far more Democratic. I think it's much more sensible as is now despite giving the Republicans an overwhelming majority. When the most sensible looking district is the only swing dustrict, you know the rest is natural. Sure, there are some odd shapes down south but they are really just changing it from pvi +30 to pvi +25. At that point, let the people get a congressman from their own party. The primary is effectively the election.

How on earth is splitting Lansing fair?

Yeah, District 8 is easily the worst part of that map (which is a pretty great example, BTW).  It looks clean but it's really a vicious gerrymander meant to sink/split the Lansing area, which by all rights ought to have its own lean-D district.

[muon2]

I was actually going to post that Michigan one too because of MI-01. I actually think it used to be gerrymandered going down to Bay County on the eastern sidea which is far more Democratic. I think it's much more sensible as is now despite giving the Republicans an overwhelming majority. When the most sensible looking district is the only swing dustrict, you know the rest is natural. Sure, there are some odd shapes down south but they are really just changing it from pvi +30 to pvi +25. At that point, let the people get a congressman from their own party. The primary is effectively the election.

How on earth is splitting Lansing fair?

Yeah, District 8 is easily the worst part of that map (which is a pretty great example, BTW).  It looks clean but it's really a vicious gerrymander meant to sink/split the Lansing area, which by all rights ought to have its own lean-D district.

The Lansing area was the impetus for the concept of urban county clusters and that they deserve consideration at the same level as whole counties. I was surprised that it became so complex to deal with it in VA for the Forum Commission, and that X didn't want it to be part of the scoring.

[Sprouts Farmers Market ✘]

I was actually going to post that Michigan one too because of MI-01. I actually think it used to be gerrymandered going down to Bay County on the eastern sidea which is far more Democratic. I think it's much more sensible as is now despite giving the Republicans an overwhelming majority. When the most sensible looking district is the only swing dustrict, you know the rest is natural. Sure, there are some odd shapes down south but they are really just changing it from pvi +30 to pvi +25. At that point, let the people get a congressman from their own party. The primary is effectively the election.

How on earth is splitting Lansing fair?

Yeah, District 8 is easily the worst part of that map (which is a pretty great example, BTW).  It looks clean but it's really a vicious gerrymander meant to sink/split the Lansing area, which by all rights ought to have its own lean-D district.

You are correct. I often missed that because Mike Rogers managed to win by double digits in recent years despite the low PVI (R+2). I assume that he rode in during 2000 and the party protected him just enough. That is pretty despicable. The whole map probably has to be redrawn  because of the city split, but District 7 should logically have Battle Creek instead.

[Sol]

I was actually going to post that Michigan one too because of MI-01. I actually think it used to be gerrymandered going down to Bay County on the eastern sidea which is far more Democratic. I think it's much more sensible as is now despite giving the Republicans an overwhelming majority. When the most sensible looking district is the only swing dustrict, you know the rest is natural. Sure, there are some odd shapes down south but they are really just changing it from pvi +30 to pvi +25. At that point, let the people get a congressman from their own party. The primary is effectively the election.

How on earth is splitting Lansing fair?

Yeah, District 8 is easily the worst part of that map (which is a pretty great example, BTW).  It looks clean but it's really a vicious gerrymander meant to sink/split the Lansing area, which by all rights ought to have its own lean-D district.

You are correct. I often missed that because Mike Rogers managed to win by double digits in recent years despite the low PVI (R+2). I assume that he rode in during 2000 and the party protected him just enough. That is pretty despicable. The whole map probably has to be redrawn  because of the city split, but District 7 should logically have Battle Creek instead.

Also, the Saginaw/Flint/Bay City district isn't quite fair either.

[Redefeatbush04]

Rather than splitlining this one makes use of an algorithm in which the average voter distance from the center of the district is minimized. I would love someone to figure out how this would impact congress   http://bdistricting.com/2010/WA_Congress/

[jimrtex]

Rather than splitlining this one makes use of an algorithm in which the average voter distance from the center of the district is minimized. I would love someone to figure out how this would impact congress   http://bdistricting.com/2010/WA_Congress/

It produces block lists.  If you had block lists for election precincts, you could convert election results to district results.   Election precincts that were split could be allocated on the basis of population.  Election precincts are small enough that there is unlikely to be a big political difference across the precincts.

[traininthedistance]

Rather than splitlining this one makes use of an algorithm in which the average voter distance from the center of the district is minimized. I would love someone to figure out how this would impact congress   http://bdistricting.com/2010/WA_Congress/

Seems to have some of the same problems as splitline... actually its problems are worse.

The New Mexico map is, in particular, a real laugher.  Let's give each district a third of Albuquerque, that's totally sensible!  And, oh god, Maryland.  Take a look at what it does around the Chesapeake.