The New York Times Upshot team came up with a dataviz that is worth your time. This is a set of maps that gives a perspective on migration patterns within the US. The metric being portrayed is the birthplace of current residents of each state.
Here is the chart for California:
I see a few smart ideas, starting with the little map on the bottom left. It servies multiple functions. It is a legend mapping colors to four regions of the US. It serves as a visual guide to the definition of regions. It serves as an interactive tool to select states. Readers might remember the use of a pie chart as a legend in my remake of one of the Wikipedia pie charts (link).
The aggregation up to regions is what really makes this chart work. This aggregation reduces the number of pieces from about 50 to about 10.
They also did a great job with the axes and gridlines. Much of the data labels are hidden but the most important numbers are retained. These include the proportion of residents who were born in their home state, the proportion of residents who were born outside the U.S., and any state(s) that contribute a significant portion of residents. In the California example, we see that the proportion of Midwest-born people living in California has declined by a lot over time.
Users can interactively hover over the gridlines to uncover the data labels.
As you scroll through the states, there are some recurring patterns.
Some states clearly have become more desirable over time. Georgia, for instance, has seen strong in-migration (colored pieces) especially from non-Southern states:
This pattern is repeated in other southeastern states, including Virginia, North Carolina and Tennessee.
By contrast, some states are not getting the migrants. As a result, the share of residents born in the home state has increased over time. The Midwestern states have this problem. For instance, Minnesota:
I also find a few states with special features. Nevada has always been a state of migrants:
Wyoming on the other hand has become popular with migrants over time but the composition has shifted away from MidWest states.
I'd have preferred presenting the charts in clusters based on patterns.
I haven't been able to figure out the multi-color spaghetti. I think the undulations are purely for aesthetic reasons.
One way to read the chart, then, is to first see three big patches (light grey for born in current state; white patch for born in other U.S. states; dark gray for born outside the U.S.). Within the white patch, we are looking for the shift between the colors (i.e. regions).