The Most Difficult States to Place in a Region

The State Similarity Index attempts to quantify how similar American states are to each other. The index is a statistically-based way to measure this. It weighs equally five major aspects of states: their demographics, culture, politics, infrastructure, and geography. The methodology is exactly the same for each state.

The data from the State Similarity Index was used to cluster American states into different regions. Some unique states, like Alaska and Hawaii, are very difficult to group with other states. Therefore, it was necessary to make the largest regions still have a great deal of variation within them. This resulted in 6 distinct macro-regions:

  1. Alaska
  2. Northeast
  3. West
  4. South
  5. Midwest
  6. Hawaii

Most states neatly fit into these regions. However, there are a few states that could easily be categorized into two different regions. Average linkage clustering does not do a good job of showing this. Averaging the amount of similarity a state has to each overall region gives a fuller picture. The following table shows the four most difficult states to classify within the 6 macro-regions of the United States:

RankStateRegion 1
Region 2


As written about in an article comparing the State Similarity Index map compared to all the regional maps of the United States created by academics, average linkage clustering seemed to misclassify Pennsylvania into the Midwest. Sure enough, when the data was analyzed, Pennsylvania was by far the biggest aberration. The Index shows it has more in common with the average state in the Northeast than the average Midwestern state. This is likely simply a fault of the average linkage clustering method. Since Pennsylvania has a lot in common with states in the Great Lakes region, like Ohio and Michigan, it got grouped in with Midwestern states. The data shows that while Pennsylvania has more in common geographically with states in the Northeast, it still has a lot in common demographically, culturally, and politically with many Midwestern states.

is pennsylvania northeast or midwest? graphic


Missouri is another state that seems to have characteristics of two different regions of the United States. Despite the fact the Missouri is almost always classified as a Midwestern state by academics, the State Similarity Index shows that Missouri could easily be grouped with Southern states as well. Missouri had once allowed slavery, unlike all the other states in the Midwest. It also required school segregation before the Brown v. Board of Education supreme court decision. Furthermore, its largest public university, the University of Missouri is in the Southeastern Conference, not the Big Ten Conference, like most Midwestern states. Another difference is that it does not ban smoking in public places.

is missouri southern or midwest? graphic


Interestingly enough, California was one of the most difficult to classify states. While it clearly should be grouped with the rest of the states in the West region, it has its own unique qualities that are far different from other states in the region like Utah and Wyoming. California also shares some significant traits with Hawaii as well. They both have beautiful beaches, warm climates, and are quite mountainous. Their culture is similar since both states have many health conscious people, so they tend to do a lot of exercise and have low smoking rates. Their governments tend to be controlled by Democrats.

what region is california in graphic


Virginia was the fourth most difficult state to group into a region, since it has traits of both the Northeast region and the South. In part, since much of its population lives in the Washington DC metropolitan area, it is wealthier and more educated than most Southern states. In addition, it is not as conservative politically. Furthermore, country music is not as popular in Virginia as in most Southern states. Being one of the most northern states in the Southeast region, its climate also tends to be colder.

is virginia northeast or southern? graphic

However, these large regions still have very significant differences within them. States as different as Utah and California are still grouped together. To account for this, the 6 macro-regions were further divided into 12 sub-regions. Even when dividing the states up into these 12 different clusters, there are some states that do not fit neatly into a region. The following table shows the four most difficult states to classify within the 12 sub-regions of the United States:

RankStateSub-Region 1
Sub-Region 2
1OklahomaSoutheast72South Central74.4-2.4
2MissouriSoutheast72.5Great Plains74-1.5
3ColoradoRocky Mountain72.8Pacific Coast72.30.5


The data from the Index clearly shows Oklahoma is a Southern state. However, its sub-region is more difficult to classify, since the state has traits of both the Southeastern states and Texas. On one hand, Oklahoma’s geography and infrastructure closely resembles Texas. Both states have a lot of oil drilling. They also generate a lot of energy from wind power. This is because Oklahoma and Texas are fairly flat and have broad plains of pasture land. On the other hand, unlike Texas, Oklahoma has relatively few Latinos. As a result, it also has a far lower percentage of Catholics. Furthermore, Oklahoma has a much higher percentage of smokers. In fact, the data shows that Oklahoma has about the same amount in common with the Southeastern states as the Great Plains states. It also should be noted that many geographers place Oklahoma into the Southwest region, but the data from the Index shows it is actually one of the least similar regions to Oklahoma.

is oklahoma southern? graphic


Not only is Missouri difficult to place in a macro-region, but it is also difficult to place in a sub-region. The state has traits of the Southeast, Great Plains, and Great Lakes regions. The southern half of the state is more like the Southeast, while the Northern half is more like the Great Plains. St. Louis has many traits of Great Lakes cities. Not only is the southern half of Missouri more religious and politically conservative, but it is also more forested and more mountainous. The combination of these factors helped make Missouri the most average state, according to the Index.

is missouri in the great plains? graphic


Interestingly enough, Colorado was one of the most difficult states to group into a sub-region. Although it is double-landlocked, it has a lot in common with the states along the Pacific Coast. Unlike other states in the Rocky Mountain region, people in Colorado tend to favor the Democratic Party and they have more liberal laws. Furthermore, it has a higher percentage of college graduates. Its people also like Rock music more and Country music less, in part because it is more urbanized than other states in the Rocky Mountains.

is colorado rocky mountains or west coast? graphic


Like Missouri, Virginia is another state that is difficult to place into both a macro-region and a sub-region of the United States. The state is on the border between the BosWash region and the Southeast region, since the Washington DC metropolitan area, is the southern-most point of the megalopolis. Still, Virginia has enough in common with the rest of the South to be classified with other Southern states and not Northeastern states.

is virginia northeast or mid-atlantic? graphic

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