Districting in the USA: Arizona

(This is part of an ongoing series. To see the other states, look for the Tag “Districts”)

As many of you know, 2021 is a year where congressional districts are drawn for the States in the USA. This occurs after a Census is done, in order to balance representation and ensure that a fairly even number of people are represented by a Representative in the US House.

Now, there are a lot of issues in general around this topic, not least that several states with only a single representative or some states with a great many can range in terms of how many people are represented. Montana, for example, has a single Representative for 1,084,225 people, whereas Rhode Island’s 2 Representatives cover 548,690 people each. This means that Montana, while having only 13,154 less people, has one less voice in the House. A system where we bring down the average (757,058) by say, capping them at 1 Rep per 100,000 persons, would give it a far more even 10 Reps each.

But that’s a systemic issue that’s a topic for a future OP.

What I’d like to focus on today is how districts get drawn up. While we all know it’s a massively political process, it doesn’t have to be that way unless we let it. I’d like to do a thought experiment where we use a simple set of rules to create districts, ignoring political party, based entirely on Population, Rural / Urban mixing, and geography.

Here are my rules:

  1. Counties should be used as the “puzzle pieces” to fill in districts. This uses already existing state delineations who already focus their efforts on a segment of the state, meaning that a town won’t have split representation based on whether we’re looking at local, state or national policies. This should reduce conflicts of policy in general and makes drawing maps easier.
  2. Districts need a population anchor. These anchors should be the most populated counties in the state, so that they represent the most people and also so that we don’t cluster the most heavily or least populated counties into the same districts. There should be a good mix this way, and give more variety of voices to very large population centers, should it cover multiple counties.
  3. Every district should be made up of a fairly equal number of people, based off of how many Representatives they have. Thus we take the population of a state and divide it by the number of Reps. This is then how many people, approximately, should be in each district.
  4. Every district should strive to include both rural and urban counties. This forces the Representatives to consider all their constituents’ needs. This also means no one can win a district by focusing only on one or two counties.
  5. Districts should attempt to consolidate in a region. This prevents weird borders and district “islands.”
  6. Counties may only be “shared” if there is no other easy way to draw districts without significant population difference. If done, it may only be halved, not cut up further. An anchor may not be shared unless it by itself is too large to be a single district.
  7. I must make these maps without consulting any political voting trends of counties or direct knowledge of existing districts.


Today we are covering Arizona. It has 9 Congressional Seats in the House of Representatives, and thus has 9 districts.

We’ll need a county map with population. I want to use the estimated data for 2019 population rather than the current census, because of the questions surrounding the data in 2020, and because I can then later compare it to the currently existing districts to see how well it matches or not. For that, I’m using this handy site with population figures per county on an interactive map:

Districting in the USA: Arizona

Based on this, we can look up the other things we need to know:

  • Population: 7,278,717
  • Representatives: 9
  • Population per Rep: 808,746
  • Most populated counties:
    • Maricopa: 4,410,824
    • Pima: 1,039,073
    • Pinal: 447,138
    • Yavapai: 231,993
    • Yuma: 212,528

If we stick to our plan, we’re going to see a lot of districts in the well populated urban center. One might be tempted to not use counties here, since they are so large (far more than say Alabama). Let’s take a look at cities:

  • Most populated cities:
    • Phoenix: 1,608,139
    • Tucson: 542,629
    • Mesa: 504,258
    • Chandler: 275,987
    • Gilbert: 267,918
    • Glendale: 248,325
    • Scottsdale: 241,361
    • Peoria: 190,985
    • Tempe: 180,587

Those numbers look more reasonable. Using each as a hub (Phoenix twice) we can build districts that are more mixed and represent different sorts of people (rural / urban).

Building Districts (1 & 2)

As the first and second anchor, Phoenix needs to be split. Since it is so close to other population centers, we need to be able to split it while not creating a wall around other centers. Unfortunately, with all the major cities practically stacked on top of one another, this is not easy. If we split it using highway 10, we can cut it off into roughly equal pieces, creating South Phoenix District (1) and North Phoenix District (2), population roughly 804,070 each. This is 99.42% of the per rep population, so it’s definitely acceptable.

So to recap:

  • District 1 includes the southern part of Phoenix, everything under Highway 10.
  • District 2 includes the northern part of Phoenix, everything above Highway 10.
  • Population is primarily urban, but grouped well together and doesn’t cut off other cities.

Let’s see how the next district goes.

Building Districts (3)

The next logical place is Tucson, but as we want to deal with the city cluster population, we’ll skip it for now. Let’s instead go to Mesa, which is itself large at 504,258. It’s wrapped around Gilbert, so it might make sense to include its 267,918 people into the mix. Adding Apache Junction (40,592) from Pinal County while cutting off Gilbert at Chandler Heights road, we get a total population of 808,768, which is 99.997% of the per rep population. Almost perfect.

So to recap:

  • District 3 includes Mesa and Gilbert, other than the lower part of Gilbert, and incorporates Apache Junction.
  • AJ gives this district some gateway into rural areas.

Let’s go on to District 4.

Building Districts (4)

Next up is Chandler, which including the area we cut from Gilbert and Chandler Heights is 351,410. Chandler is also somewhat wrapped around Tempe, so let’s add their 180,587 to the mix. Throw in Sun Lake (14,473) and the Highway 60, 79 and 87 loop, and you get 809,403 people (cutting off 123,112 from Pinal County) and coming up with a total of 100.08% of the rep population.

  • District 4 includes Chandler, Tempe, parts of Gilbert and the rural highway loop around San Tan Valley.
  • It eats a bit into a different county.
  • There is a sizable rural population here, mixed in with the fourth largest city.

Let’s go to District 5

Building Districts (5)

Glendale (248,325) is next, and it’s got its back to Phoenix and is almost eating Peoria, so let’s just add it (190,985). If we add in the rest of the west and south Maricopa County, we add 373,436 people, creating a district with 812,746 people. This is 100.49% of the rep population.

To recap:

  • District 5 includes Glendale, Peoria and the rest of south and west Maricopa County.
  • Population is a good mix of rural and city.

Let’s go to District 6

Building Districts (6)

Last of the center districts is Scottsdale (241,361). If we add the last bits of Maricopa county (North and East) to this, we get a population of 811,077, which is 100.29% of the rep population.

To recap:

  • District 6 is Scottsdale and all the surrounding area in Maricopa County.

Building Districts (7)

Finally it’s time for Tucson (542,629). So far we haven’t done anything with the other counties aside from cutting some from Pinal. Now we’re going to trim a bit from Pima county, enough to create a district around Tucson and leave some over for the last two. First, we will slice a bit off the West end, close to Yuma County, that comes up to around 67,000 people. Next we cut a “V” into the top of Pima, from highway 10 to highway 77, starting at Casas Adobes. This leaves us with 812,907 people, 100.51% of the rep population.

To recap:

  • District 7 is Pima minus a small chunk in the West and a V in the top.
  • Population is a good mix of rural and urban, possibly the best mix of all the districts, while still having a strong central hub.

Building Districts (8)

Yuma (95,548) will anchor District 8, running up the west side of Arizona. We mix Yuma county (212,218), La Paz (21,098), Mohave (209,550), Yavapai (231,993), and Coconino (142,854), without Flagstaff (76,831). We also need a bit from the south (67K leftover from Pima County). This creates a district that runs up the west side and half of the north, and has a population of 808,713, which is 99.996% of the rep population.

To recap:

  • District 8 includes five counties, mostly rural, and encompasses the West and North of the state.

Building Districts (9)

Flagstaff (76,831) anchors this district, picked out of Coconino County because of its size. No other large city is left, so we need to be sure that this isn’t just rural. In addition, there is a lot of Native land in this area, so we want to ensure that people are represented properly. This means we add Gila, Navajo, Apache, Greenlee, Graham, Cochise, Santa Cruz, what’s left of Pinal County and the upper V of Pima county, and we get 806,963 people, or 99.78% of the rep population.

To recap:

  • District 9 takes the leftover area from Pinal and Pima County, as well as Flagstaff from Coconino, and mixes it in with the smaller East counties.
  • There is a mix of urban areas and rural areas
  • A lot of land is Native land

Final Picture

While we weren’t able to keep exactly to each rule specified above, we stuck well to the principles and made districts that are both condensed geographically and represent a good mix of the population. Counties were hard to use as they were so large and often we had to go on the basis of city size. Even that was difficult, as many “cities” are actually just urban areas of Phoenix. Based off of our construction above, we get a map that looks like this:


Right now, the districts in Arizona look like this:

The Southern District is cut by the Native territory, and picks up from slices of Maricopa, Pima, Pinal and Yuma, as well as the entirety of Santa Cruz. The other border districts (1 and 4) all cut into the cities (Tucson and Phoenix). This is not condensed, nor geographically relevant. It’s mainly done to cut up the city. Inside the city the districts don’t look very different.

Arizona is a tough state to district, but I think our map is far better in terms of simplicity, mix of population while still retaining the interests of the geographical area and those who live there. Additionally, anchoring them in various large cities is far superior than cutting two large cities up in so many districts, as it gives each district more weight while allowing the central hub of population to concentrate their interests, as they should.

What do you think? Which map do you think makes more sense? What rules would you implement? What would you value and/or like to see? Let me know in the comments below!

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