Which Congressional Districts are Over and Under Populated

Which Congressional Districts are Over and Under Populated

The foundation of the U.S. democratic system is based on fair representation of its residents. The story of representation is complicated, hard-fought, and still evolving. Currently, representation through the 435 Congressional districts is decided in elections every two years but districts are redrawn every ten years after the decennial Census is conducted. Districts are drawn by states to have exactly equal, or as close as possible, number of people within the boundaries of each. That population is determined from dividing the state’s population by the number of districts, producing a number sometimes called the target or ideal population.

But population constantly shifts and changes in between when districts are redrawn, causing some districts to be what we’ll call “over” or “under” populated. Overpopulated districts have grown faster than the state as a whole and have more people than ideal. Underpopulated districts have grown slower than the state, or even declined in population, and thus have fewer people than the ideal population for fair representation.

View the full-screen interactive version.

Over and under populated

Using the latest U.S. Census Bureau estimates, we mapped the over-and-under population of Congressional representation across the country. For each state, we calculated the target population (state’s population divided by the number of districts). We styled the districts by the percentage over or underpopulated. Click on a district for more information about it in relation to each district in its state.

What it tells us about representation

How equal are Congressional districts supposed to be? Exactly equal, if possible, with only as much as one person deviation among districts, ever since Vieth v Jubelirer in 2004. This is, of course, an unmaintainable standard in between decades, as the population has changed even before the districts go into effect. Even when districts are redrawn mid-decade, such as recently in North Carolina, they are instructed to use the 2010 population data.

Nevertheless, it can be an interesting exercise to look at representation of the most over and underpopulated districts.

Most over populated districts

As it turns out, the 10 most over and underpopulated districts are represented evenly by Republicans and Democrats.

Most under populated districts

The 10 most underpopulated districts are also represented evenly by Democrats and Republicans.

What it can predict for redistricting

The process for redistricting varies by state. In most states, the legislature is in charge of redrawing Congressional districts. A handful of other states have independent or citizen-led commissions tasked with redrawing the map. However, in every case redistricting will be impacted by two factors: the state’s population and the current districts. The state’s population will determine how many representatives are reapportioned and then must be drawn into districts. The population will determine how those districts are shaped and formed. If a state’s delegation is favorable to whichever party is drawing the districts, it’s likely there won’t be much in the way of radical change – districts that are underpopulated will grow in size and districts that are overpopulated will have to shrink somewhat. They’ll try to keep the same or even better electoral outcome for the party.

Though the most overpopulated districts are represented evenly by Democrats and Republicans, the fastest-growing parts of the country the past decade have been the suburbs – whose voters are trending Democratic. For redistricting, it might mean that if Republicans are trying to gerrymander they will create more rifts and splits in suburban communities, dividing them while keeping rural areas whole. Democrats might do the opposite, dividing the rural areas to make sure that city and suburban voters will outnumber them in districts. A large part of the Democratic trend in the suburbs is a result of increasing diversity, which will also have implications for how districts are redrawn. More majority-minority districts and minority opportunity districts will surely have to be drawn, particularly in states like Texas.

The 22nd Congressional District in Texas, the most overpopulated, is a rapidly diversifying area sprawling south of Houston. Donald Trump won this district by eight points in 2016, down from Mitt Romney’s substantially larger 25 point win in 2012. The district is represented by Republican Pete Olson, who announced last year that he is retiring at the end of his term.

How we made this map

We used the Dirty Reprojectors library to reproject the Congressional district data into the Albers USA projection. The road, urban area, and city data from Natural Earth were used to add some context to the map. We built the interactive graphic using React function components and hooks and starting with the create-react-app template. The panel was created using the React Vis library from Uber and the map was created using Mapbox GL JS. Check out the github repository here.

What this map doesn’t show

Congressional representation is reapportioned every ten years. We wrote about this last year. Some states, like Texas, are expected to gain Congressional representation and therefore districts after reapportionment. Unlike states that will have the same number of districts before and after, redistricting may not necessarily shrink those overpopulated districts. That’s because the state’s target population for districts will be adjusted to take into account a greater number of districts. There, you will see additional districts added – likely in high population growth areas. 

Our redistricting and gerrymandering work

Azavea has a long history of working on projects related to redistricting, gerrymandering, and elections. We’re excited to launch DistrictBuilder later this year and offer consulting services for redistricting preparedness. Contact us if you are interested in redistricting consulting or sign up to receive updates on DistrictBuilder.