Methodology

How Was This Database Built?

Census data is reported by geography, such as political districts, statistical areas, or special-purpose polygons such as ZIP Codes, or metropolitan areas.

Change is inevitable with any geographic area—political or statistical. Most of the changes result from boundary revisions. Even if boundaries don't change, the Census Bureau may renumber the geocodes with a new census, for examples such as the change from three-digit block numbers in 1990 to four-digit codes in 2000.

All of these changes preclude simple comparison of the numbers from Census 2000 to data from the 1990 Census. The only way to compare the data is to define a correspondence between the geographic areas in each census. To enable this comparison, ESRI carefully translated the 1990 Census data to correspond to the geographic areas in Census 2000.

An example of a more detailed discussion of ESRI's 1990-2000 race analysis is the white paper Trends in the U.S. Multiracial Population 1990–2000 [PDF-657 KB, 24 pages].