[1] Tract boundaries and income data were taken from the GeoLytics/Urban Land Institute Neighborhood Change Database, in which data are "normalized" to 2000 boundaries. Because the algorithm used often requires that data from thinly populated areas in the earlier years be distributed among several tracts, it is likely that there are some errors in the edge of the urban region.

[2] Income data have been converted to constant dollars using the consumer price index.