Examples of our unbiased district-drawing algorithm in action / comparisons with gerrymandered districts drawn by politicians

(Executive summary) (Return to main page) (splitlining pictures for all 50 states)

Advantages

The advantage of having our simple splitting algorithm draw the congressional districts is obvious. There is one and only one drawing possible given the number of districts wanted, the map of the state, and the distribution of people inside it. Which of those people are Liberal, Conservative, Republican, Democrat, Black, White, Christian, Jewish, polka-dotted, or whatever has absolutely zero effect on the district shapes that come out. So you know the maps are going to be completely unbiased. Get politicians to draw the maps and you know that not only are they going to be completely biased, they are also going to be a heck of a lot more complicated-shaped and they are going to use up a lot of your taxpayer money figuring out how to best-rob you of your vote. Which do you prefer? It has been over 200 years. Isn't it time to make gerrymandering a thing of the past?

The shortest-splitline algorithm for drawing N congressional districts (part of our ballot initiative)

Formal recursive formulation

Start with the boundary outline of the state. Let N=A+B where A and B are as nearly equal whole numbers as possible.

(For example, 7=4+3. More precisely, A = ⌈N/2⌉, B=⌊N/2⌋. ) Among all possible dividing lines that split the state into two parts with population ratio A:B, choose the shortest. (Notes: since the Earth is round, when we say "line" we more precisely mean "great circle." If there is an exact length-tie for "shortest" then break that tie by using the line closest to North-South orientation, and if it's still a tie, then use the Westernmost of the tied dividing lines. "Length" means distance between the two furthest-apart points on the line, that both lie within the district being split.) We now have two hemi-states, each to contain a specified number (namely A and B) of districts. Handle them recursively via the same splitting procedure.

Asterisk: If anybody's residence is split in two by one of the splitlines (which would happen, albeit very very rarely) then they are automatically declared to lie in the most-western (or if line is EW, then northern) of the two districts.

Pictures, Video

C.G.P. Grey's 3.5-minute youtube video attempting to describe the shortest splitline method.

High-precision computer-generated pictures for all 50 states, with commentary and analysis.

Compare the pictures

Tennessee's 9 congressional districts (pdf; as they were in 2004) Don't you love the incredibly gerrymandered shapes of districts 3 and 7? (No House member from Tennessee ever lost a bid for re-election during 1980-2005.)

Great. Now compare with our approximate sketch (png fastest ) (tiff second best ) (pdf third ) (ps) of how they'd instead look as drawn by our completely bias-free automatic splitting algorithm.

Arizona's 8 congressional districts (pdf; as they were in 2004) Yes! We have a new champion for most incredible gerrymander: district 2.

Great. Now compare with our approximate sketch (png fastest ) (tiff second best ) (pdf) (ps) of how they'd instead look as drawn by our algorithm.

North Carolina's 13 congressional districts (pdf; as they were in 2004); love that district 12, and hello, district 3 actually is divided into two or three pieces since it goes out to sea and comes back to land! Or maybe two of them are connected at low tide? (Was that what Paul Revere had in mind when he said "one if by land, two if by sea"?) And ooh, check district 1!

Great. Now compare with our approximate sketch (png fastest ) (tiff second best ) (pdf) (ps) of how they'd instead look as drawn by our algorithm.

Massachusetts''s 10 congressional districts (map from Adam Carr's Psephos archive) (gif fastest) (png middle) (jpg slowest) versus approximate sketch of how it would look redrawn with our algorithm: (png fastest) (jpg slower) It was Massachusetts governor Elbridge Gerry who is credited with inventing gerrymandering in 1812. He was voted out of office immediately by outraged voters, but his legacy evidently lives on. Massachusetts has 100% Democratic congressmen and has for at least the last three election cycles, despite having a Republican governor (you can't gerrymander the governor race, since it is a statewide election). Here's a Boston Globe Editorial on the subject.

Texas's 32 congressional districts (side-by-side comparative chart from the Associated Press as printed in the Houston Chronicle 9 Oct. 2003) showing district shapes before and after the extraordinary redistricting in 2003. (jpg) (And here [png] is a closeup on what they did to Austin to split up those annoying Austin voters.) The gerrymandering was not inconsiderable before the redistricting, e.g. check district 4 near Dallas. But, after it – after it – aaah, for total statewide brazenness Texas really takes the cake. Check district 19 (Lubbock in the north West) and the whole East half of the state is made of those long thin districts. And for extra amazement check those closeups on Houston, and Tom DeLay's personal district 22. Yup, definitely Texas is an unbelievable new champion. (Check the 127-page Texas Court decision declaring this totally legal. Before re-gerrying: Texas had 17 Democrat and 15 Republican congress. After, it was 11-to-21 the other way. Christian Science Monitor editorial on this.)

(You can make your own sketch of what Texas would look like with the new scheme. Have fun. Much nicer, no?)

Maryland's 8 congressional districts (gif; as they were in 2004). Holy sea of rattlesnakes Batman! Numerous go out to sea and come back to land districts, amazingly squirelly boundary shapes. Here's approximately how it would look redistricted via shortest splitline (png).