opinion of using 'shortest splitline' algorithm for districting

[muon2]

I don't like it for districts. Among my complaints:

It ignores any natural geographic features - it hops mountains and rivers in ways that ignore connectivity.

It splits existing political boundaries for counties and municipalities in ways that needlessly complicate elections and increase cost.

It tends to carve through major metro areas and if mapped at the level of whole census blocks it would appear just as ragged as some gerrymandered districts.

It surrenders compactness for minimum line length.

It fails in any state subject to the VRA.

[muon2]

Haha, oh wow, this algorithm really does hate keeping cities intact.

Medians are more probably to occur in areas of higher density.

The east-west median of population got stuck in the Detroit/Indianapolis area for 50 years or so, even as the mean continued moving westward.

True. The median is a point that only reflects how much of the data lies one either side of that point. The relative distance to that point does not matter, even though it would in the mean (or average). The median will either be at one of the data points or midway between two points if there are and even number of data points.

Since the median is located at a specific data point, the likelihood of it's occurrence is tied to the likelihood of finding any data point in general. That is the median is more likely to be at a part of the data set where data is more densely clustered. For the 2-D problem of the splitline algorithm, this means in areas of higher population density, ie cities.

[muon2]

In discussions about split line, one suggested alternative metric would be to consider density in the measure of the length of the cut line.  Lines that cut through less dense areas would be favored.

This is a pseudo-splitline.  I first sliced blocks into 11 equal-population slices based on longitude.  These were regrouped into a 3:4:4 pattern (based on less density to the west, and then resplit based on latitude.

http://www.redrawsf.org/

Click on View District Maps

Click on "Check 2010" map.

Be patient with the refreshes.  You can't interact while the map is repainting.  So when you zoom in, click on 3 or 4 steps up on the zoom bar, rather trying to drag the indicators.

The process makes more sense in an urban area where there is less variation in pop density. The uniformity in density shows up as districts that cover roughly the same amount of area. I'd still like to see this type of modified algorithm use the underlying street axes, so that the lines are less erose.

[muon2]

IIRC you had a version some time ago where you took a splitline but then adjusted it to conform to the nearest county (or municipal) lines. This seemed to me like a preferable implementation of the concept since it corrects for political subdivisions while maintaining the core idea of splitline.