The Research Group's blue map allows users to select the "leave from" metro area and then maps where people move to. So in the example below, the data shows that those who left the Hartford, CT area between 2009 and 2013 largely stayed in New England, and in fact, the vast majority simply moved to another part of Connecticut. (Why Hartford as a starting place? I spent some of my formative years in West Hartford.)
With the Research Group's red map, users select the destination and the map shows were people come from. In this example, the destination is the Washington, DC metropolitan area.