The heavy solid black line indicates the city limits of Chicago. The thin dark grey lines are census tract boundaries. The blue lines are freeways. All 2010 statistics have been recompiled to fit 2000 tract boundaries, generally by assigning 2010 data to the 2000 tracts in which 2010 tract centerpoints fell. This should present no great problem where tract boundaries were unchanged or where tracts were split, conditions that apply to ca. 98% of the census tracts in the Chicago area. In cases where more complicated tract boundary changes occurred, it is likely that the maps err in small ways. The location of dots within tracts is random.