Base Year Data: The base year population data is derived from the 2000 Census of Population and Housing. Although the Census Bureau conducts periodic estimates of population by governmental unit, the 2000 Census is the only source of population data available at the census block level. Utilizing ArcView GIS, base year population data at the zonal level for 2000 was derived from the area proportion allocation of block level population to TAZs.

Future Year Data: As a tri-state regional planning agency, OKI uses county level projections as prepared by the respective state data centers (Ohio Department of Development Office of Strategic Research, Kentucky State Data Center and Indiana Business Research Center). Projections currently being utilized were released by the respective state data centers in 2003. Population projections at the zonal level are calculated based on expected future year changes in household size and applied to the projected zonal households.