The result is impressive, the lines chosen look reasonable (I’ve not had time to go carefully through the whole diary), and the categorization of the process by which the lines were drawn for each state alone is pretty helpful.

The diary is here: http://www.dailykos.com/story/2013/04/22/1201551/-Did-Gerrymandering-Cost-Dems-the-House-A-33-State-Look-at-Alternative-Non-Partisan-Maps

The conclusion is that if the lines were drawn by a California-style commission, there would have been a Democratic House majority in 2012.

I have to admit that I embarked on a similar project, but though my maps are finished, and I’ve downloaded the relevant demographic and political data into a series of spreadsheets, I haven’t gone through the spreadsheets yet to see what the political effects were (I have a day job).

However, my project was different. The neutral redistricting model I used was the British boundary commission, with the exception that I used the American rules for deviations from the mean for the size of populations in each district. But I decided to ignore the Voting Rights Act and instead strictly avoid crossing local government boundaries (mainly county boundaries), as much as one could given the low American tolerance for population deviation, and otherwise use communities of interest. One of the reasons I took this approach was that with the entire VRA up for review by the Supreme Court, I was curious to see how many majority African-American and majority Latino districts could be drawn using purely race-neutral criteria. Though racial criteria comes back in to some extent with communities of interest, the provision of avoiding crossing local government boundaries makes it really difficult to get to 50% +1 voting age populations for various racial groups.

There is right now about an equal likelihood of the US adopting the British or Canadian methods as taking the California approach, the likelihood of both happening in the near future being zero.

However, the “respect local boundaries” approach itself leads to some oddities, since in the US local government boundaries too are often gerrymandered.

I do have some other issues with the diarist’s approach. First, the actual California process was not as neutral as he seems to think, the Democrats were more effective in lobbying/ manipulating the commission (this has been documented) so the resulting map should be characterized as a Democratic-friendly commission map, similar to Arizona. This means that a less Democratic-friendly commission, say on the model of Washington, would not necessarily have produced a map resulting in a Democratic majority.

My other issue is with the assumptions that the maps drawn by judges are both politically neutral and would duplicate the maps drawn by a commission, both of which are highly questionable for all sorts of reasons. I redrew the judge-made maps as well.

Even with these big differences in approach, the diarist’s maps came out quite close to mine. The whole diary and comments are worth taking the time to go through, and also with redistricting software now available to the general public, there really should be more interest by political scientists in map-making.

House districts with margins of less than 5%, by party:
R 27
D 21

Of less than 2%:
R 12
D 10

(Partially transplanted from a previous thread.)

Manuel, if you do come across the 2012 CD-level results, I’d like to see them!

Under the existing system, Romney could have won the election had he prevailed in the three most closely fought battleground states – Florida, Ohio and Virginia, with a total of 60 electoral votes – plus New Hampshire, whose four electoral votes would have put Romney at the bare minimum majority of 270-268. This could have happened had less than 250,000 voters in the aforementioned states switched from Obama to Romney…which nevertheless would have left Obama with a sizable popular vote lead over Romney.

Now, in addition to the described changes, let’s suppose that Virginia had also adopted the “GOPmander” plan for the allocation of its 13 presidential electors. As it happens, even if Obama lost that state, he would still prevail by large margins in three of its eleven CDs…and in the process deprive Romney of an Electoral College majority: Obama would then retain the White House by 271-267, with the Virginia “GOPmander” backfiring disastrously on the Republican Party.

Incidentally, this is probably not the only scenario of its kind, but I haven’t come across full CD-level 2012 presidential election results to confirm another example I have in mind.

For purists (like me!) I also prepared a version with the actual vote percentages. The overall pattern remains the same.