A digital map of Public-Use Microdata Areas in the 1990 U.S. census.

"Public-Use Microdata Areas (PUMAs) are the smallest geographic units for which many U.S. Census variables are reported. In particular, 1990 microdata records for households and individuals can be aggregated only by PUMA, metropolitan area, state, and region. The Census Bureau distributes maps of these PUMAs only on paper, however, and only for individual states. This note describes the construction of a national, digital base map of the PUMAs used in the 1990 U.S. Census microdata files (5% sample)."