There were many changes in the boundaries of tracts between the 1990 Census and the 2000 Census. All 2000 statistics have been recompiled to fit 1990 tract boundaries. This presented 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. This problem was only common in northern Lake County, Illinois, and in Lake County, Indiana.