Stratifying neighborhoods

Sociologists Kendra Bischoff of Cornell and Sean F. Reardon of Stanford have tracked the growth in economic segregation in the 117 largest metro regions in the country. First, they sorted every census tract in those regions into one of six categories based on median family income. Then, they charted the rising number of poor and affluent tracts over time. The Globe mapped three regions in eastern Massachusetts — one stretching from Revere into Boston and points south; Essex County to the north of Boston; and Middlesex County to the north and west.

Affluent (150%+ of area median)
High income (125-150%)
Upper middle income (100-125%)
Lower middle income (80-100%)
Low income (67-80%)
Poor (Less than 67% of area median)

SOURCE: Kendra Bischoff, Cornell University, and Sean F. Reardon, Stanford University, using decennial US Census data from 1970, 1980, 1990, and 2000 and American Community Survey five-year estimates for 2005-2009 and 2010-2014.

David Butler, Patrick Garvin/Globe Staff