Today we’re going to look at the same Census place-of-birth data as my earlier post. But this time, instead of looking at the state level, we’ll drill down to something called a Census Tract. A census tract is a small, usually permanent geographical division. Typically their population ranges between 1,200 and 8,000, with an optimum size of 4,000. There are about 73,000 census tracts in the United States. They’re a nice way of looking at data below the state level, since the population from tract to tract is pretty similar. This gives them a distinct advantage over counties, whose size is totally arbitrary and who can range from huge to tiny (Los Angeles County: 10 million people; Loving County, TX: 169). Census tracts aren’t all exactly the same population, but they are usually pretty similar.
As an example of census tract sizes, here are the tracts of Santa Cruz, with the one I live in highlighted blue.
It’s one of a dozen or so tracts in the city of Santa Cruz; the entirety of Santa Cruz County consists of 53 tracts. As you can see they are pretty granular.
The US census’ Annual Community Survey tabulates lots of information at the Census Tract level, including the place-of-birth data we looked at previously. Let’s have some fun with that.1As I mentioned last time, the data from ACS are estimates based on surveys of a subset of all households. Since tracts with tiny populations have a good chance of generating spurious data, those with population below 100 are ignored.
First question: which census tract has the highest percentage of residents who were born in state? That would be Census Tract 9505, Evangeline Parish, Louisiana. Part of the city of Ville Platte, in central Louisiana. 98.1% of its 3063 residents were born in Louisiana. It ticks all of the boxes for not having a lot of migrants from other states: rural, relatively poor, and located in the middle of the state. [Surprisingly (or not surprisingly if you think about it), census tracts near state borders tend to have a higher percentage of migrants from other states – in those cases, it’s people from the nearby state moving a few miles across the border. If someone moves a few miles to Ville Platte, they are still originally from Louisiana; if they move a few miles to a border census tract, there’s a chance they’re from another state. It’s just an artifact of geography.]
The rest of the top ten “homebody” census tracts include several others in Louisiana, and a few in other southern states. Basically places with no particular draw (either economic or retirement) for migrants. There may be plenty of good reasons to live there (Ville Platte has significant Creole and Cajun influences, and is known for its smoked meats and swamp pop music), but they aren’t really draws for the outside world.
What about the other end of the spectrum, census tracts with the fewest number of residents born in state? Here are all of the tracts with less than 1% natives:
| Tract | Natives |
| 4202.13, Maricopa County, Arizona | 0.46% |
| 405.28, Maricopa County, Arizona | 0.47% |
| 57.16, Clark County, Nevada | 0.52% |
| 9801, Hardin County, Kentucky | 0.55% |
| 104.03, Broward County, Florida | 0.62% |
| 57.14, Clark County, Nevada | 0.71% |
| 8.02, Sarasota County, Florida | 0.75% |
| 17.04, Manatee County, Florida | 0.90% |
| 59.40, Palm Beach County, Florida | 0.96% |
The tracts in Arizona, Nevada, and Florida are all retirement communities, so there’s no surprise there (although the “born here” percentages are remarkable – only 1 of 200?!) But what about Hardin County, Kentucky? Another retirement spot? Nope, that tract represents the personnel at a military base (Fort Knox, actually), who are typically from all over the US. There must be a few locals who work on the base; I guess they live in a different census tract.
When it comes to place-of-birth, what areas of the United States look most like the US as a whole? First we have to define what the US looks like as a whole. Here are the percentages
| Birth location | US Average (% of population) |
| Born in a different US state | |
| …in Northeast state | 6.3% |
| …in Midwest state | 7.1% |
| …in Southern state | 8.3% |
| …in Western state | 5.0% |
| Born in a different country | |
| …in Latin America | 6.9% |
| …in Asia | 4.2% |
| …in Europe | 1.5% |
| …in Africa | 0.7% |
| …in Canada | 0.3% |
| …in Oceania | 0.1% |
I’ll compare each of the 73,000 census tracts to these numbers., and choose whichever is closest to these percentages2Technically, the lowest residual sum of squares. And the winner is: Census Tract 9201.11, Los Angeles County, California (in Santa Clarita). A typical middle class suburban California neighborhood. Here are it’s numbers, compared to the US average:
| Birth location | US Average (% of population) | 9201.11 (Santa Clarita) |
| Born in a different US state | ||
| …in Northeast state | 6.3% | 5.7% |
| …in Midwest state | 7.1% | 6.9% |
| …in Southern state | 8.3% | 8.5% |
| …in Western state | 5.0% | 4.6% |
| Born in a different country | ||
| …in Latin America | 6.9% | 5.0% |
| …in Asia | 4.2% | 3.2% |
| …in Europe | 1.5% | 1.6% |
| …in Africa | 0.7% | 0.7% |
| …in Canada | 0.3% | 0.0% |
| …in Oceania | 0.1% | 0.0% |
That’s remarkably close to the US average. Second on the list is a tract on the western edge of Escondido, California; again, a typical California suburb. In fact, out of the top fifty, 28 are in California, and 15 are in Texas (in the Houston, San Antonio, and Ft. Worth areas). But while California has a majority of the most similar tracts, it also has quite a few of the least similar. This is because there are regions of the state that have huge quantities of immigrants from other counties (typically, Latin America or Asia) – way more than the US average of 14%. As a whole, California doesn’t reflect the place-of-birth demographics of the nation – it has way fewer migrants from other states, and way more from other countries. But there are hundreds of smaller enclaves within the state that do match what America looks like. Of the 500 census tracts that are closest to the national place-of-birth averages, more than half are in California.
So does California look like the rest of the nation? Like most interesting questions, the answer is complicated. And I think it’s safe to say the answer is: yes and no.
