In our previous blog, we have discussed how census tract boundaries can be changed after the release of the 2020 Census, and why it matters, and in this blog, we continue the discussion by looking at the census tract boundaries changes in Michigan and specifically, in Detroit. In short, accurate Decennial Census counts provide the basis for redistricting and funding, which are determined and impacted by geographic boundaries called Census tracts. Thus, for urban data users, knowing census tract boundary changes is important as these changes can raise an early indication of significant demographic changes, such as population, housing units, race/ethnicity composition.
Census Tract Changes in Michigan
Now, let’s take a look at the census tract boundary changes in Michigan, in 2020, and see how geography changes are associated with population changes.
In 2010, there were only 2,814 census tracts in Michigan, and in 2020 there are 203 more census tracts, adding up to 3,017 census tracts in total. The actual changes are far more complicated.
Here is a quick review of D3’s definitions of all changes (new, split, combined, expanded, and shrank), as shown in the interactive map above:
Split census tracts are new tracts that are created by splitting a single census tract into two new geographies. These changes are typically associated with significant population increases.
Combined census tracts are new census tracts that are formed by merging two or more established census tracts into single geography. These changes are typically made due to a significant decrease in population across neighboring tracts.
New census tracts are created by merging only portions of established Census tracts into new shapes. These might be the result of a shift in population that is disproportionate across the original geography.
Expanded census tracts are the ones that have a larger geometric shape and geographic size than their 2010 counterparts.
Shrank census tracts have a smaller shape and size than their 2010 counterparts.
Taking all changes into account, 527 old census tracts have been modified, which account for roughly 1/5 (18.7%) of the 2010 census tracts.
To break down these changes, we can now scrutinize them at the county level. Southeastern Michigan, particularly Wayne County, stands out with significant changes. There are 448 new census tracts (2020) that were created by splitting the 2010 census tracts, and most of which are in lower Michigan: 69 split census tracts are in Wayne County, 52 in Macomb, 34 in Kent. Meanwhile, there are only 27 new census tracts created by combining two or more 2010 census tracts, most of which are also in Wayne County, especially in Detroit. Moreover, some new 2020 census tracts were created by combining portions of several 2010 census tracts, which are labeled as “New” instead of “Combined” in our interactive map. There are 20 “New” census tracts, and they only exist in Wayne, Oakland, and Washtenaw.
Several major population growths at the county level match with our observation: Oakland County added the most residents overall, increasing by 72,033 residents. Kent County grew by 55,352 people, followed by Macomb County, which added 40,239 new residents.
However, it’s insufficient to conclude that Wayne County’s population has grown as there are more “split” census tracts than “combined” ones. We noticed that some split census tracts were created when an unpopulated area needs to be excluded from a populated area—for instance, a park and a neighborhood that used to be in one census block could now be split apart in 2020 for census purposes, therefore changing the boundary of the census tract that the block belongs to.
In fact, as 2020 census data shows, Wayne County’s population continues to shrink with a loss of 27,023 residents from 10 years ago. Detroit, in particular, has lost 74,666 residents. However, the huge loss in Detroit was offset by gains in other parts of the county. Dearborn’s population grew 12%, from 98,152 to 109,976, and that of Canton Charter Township grew 9%, increasing from 90,173 to 98,659.
Census Tract Changes in Detroit
Detroit’s population is still shrinking for the 7th decade, but the speed has slowed down.
In Detroit, “combined” 2020 census tracts have outnumbered “split” ones by four to one (32 vs. 7). “Split” census tracts are only found in the Southwest Detroit, Dexter-Linwood, and River Rouge neighborhoods. “Combined” census tracts are more scattered across the city, mainly located on the east side of Hamilton Ave and the north side of Grand River Avenue. Two census tracts were once completely within the city boundary, and now cover up parts of areas in Redford and Dearborn to get enough population for the threshold. While Detroit lost 10.5% of its population from 2010 to 2020, it once lost around 25.0% from 2000 to 2010.
The geography and population changes mentioned in this article are only scratching the surface, as more 2020 data are to be released this September. D3 will keep updating blogs and data reports to help Detroit communities to know in time how demographics have changed in the past decade and why the impact will be.