Because I had a bit of time on my hands yesterday, I decided to quickly put together another map of the changes in population density in metro Detroit. But this time, instead of looking at absolute density changes like I did in the original map, I thought I would see if I got a different look when I examined these changes on a percentage basis. Take a look at the results here.
Let’s start in the suburbs. Even though most of the suburban areas are still relatively low-density, we can see that many of them have at least doubled in density since 1970. Of course, since they were starting from a fairly low population density in an absolute sense, even doubling or tripling that density isn’t enough to push them into the “more dense” category (i.e., orange or red shading) on the original, decade-by-decade map.
If you’d looked at this newer map showing percentage changes in density first, you might conclude that Detroit has pretty dense suburbs. But even though some of those areas have seen densities increase by five thousand percent (yikes – some of those tracts must have been empty in 1970), we can still see from the original map that Detroit and Wayne County are more dense, in an absolute sense, than almost the entire suburban zone.
This is a good example of why it often takes more than one map of the same data to tell the whole story. Both of these maps give a very different impression about suburban density in the Detroit metro area; the full story only makes itself clear when you look at both absolute densities and percent changes.
Unfortunately, both maps tell pretty much the same story about the city of Detroit itself. It has hemorrhaged population since 1970, in both an absolute sense and a relative sense – what astounds me is that some tracts in Detroit have seen population densities decrease by upwards of 90 percent. No matter how you slice the numbers, you always end up in the same place. And it ain’t a pretty one.
Here endeth the lesson.