I'm thinking there is more to it than what you've outlined. If the 188 people are, on balance, younger, one would expect a lower per capita income. Which would make the trade a horrible one. Consider, 188 young hungry twenty to thirty five year old men and women, for 151 forty to fifty year old men and women. I think if I'm Atlanta, I'm comfortable with that trade.

I think the Southern cities are doing a good job attracting a more youthful demographic. Click on Harris County in Texas, (Houston). I think it is probably the 'blackest' on the map. Most of the people moving there have lower incomes. Yet at the same time they just elected an openly lesbian woman, with an adopted black daughter as mayor. I think there is a lot of evidence like this that massive numbers of young, hungry and educated people are probably moving in to Houston.

And yet.

I think the best places to move to, are probably the ones that everyone else is moving from. For instance, I would wager that the blacks and whites moving in to the Detroit area are of a higher economic quality than the blacks and whites moving out of the Detroit area.

Your material point is correct however. We need more information to make any determinations about whether what the map tells us is promising or troubling in economic terms. I would just expand the information you cited to include more than just income. In fact, I think it is more important to know age and educational level.

"For instance, I would wager that the blacks and whites moving in to the Detroit area are of a higher economic quality than the blacks and whites moving out of the Detroit area."

I couldn't get to the map (I'm just getting loading dots forever), but: As I sometimes have to tell people who don't live around here, while Detroit is every bit the sucking cesspool you've heard of, the greater Detroit metropolitan area is actually full of relatively upscale and nice places to live. It even has many businesses that aren't related to the automobile industry, though not enough. Detroit proper is physically huge, preventing this area from being called the greate Southfield/Novi metropolitan area. My guess is that virtually nobody is moving into Detroit itself, but that there are still some things in the same county and certainly in the surrounding counties that might see some people moving in. Net loss, of course, but there's always some people moving somewhere.

Boston is in Suffolk County