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As part of the Census 2000 geographic product series, the Census Bureau has produced Census Tract Relationship Files. (In previous censuses, this product was called a comparability file.) These files show how 1990 census tracts relate to Census 2000 census tracts. The files consist of one record per each 1990 census tract/2000 census tract spatial set. A spatial census tract set is defined as the area that is uniquely shared between a 1990 census tract and a 2000 census tract.
The Census Tract Relationship Files consist of four sets of files. The purpose of these files is to assist users in determining the relationships between 1990 and 2000 census tracts. Two of these files are state-level entity based census tract relationship files. One file provides a measurement of change based on population; a second measures change using street-side mileage. The other two files specifically list census tracts that have experienced significant change: one file from the perspective of 1990 census tracts, the other from the perspective of Census 2000. All four census tract relationship files will be available for each state-level entity as well as at the national level.