Census Block Population Estimates: Purpose and Practice

Michael S Mohrman, State of Washington
Kyle Reese-Cassal, State of Washington
Theresa J. Lowe, State of Washington

Washington’s Forecasting Division has developed a program for small area population estimates in response to increasing demand from state and local governments. This program combines local building data, the georeferencing capabilities of a GIS with the division’s established city and county estimates program to produce population estimates at the census block level. Block data are then aggregated into special area estimates, which fulfill statutory requirements, establish population based taxation rates, and help evaluate state and local programs and policies. Advancing simple housing unit methods, this program is continuously updated with local building data as it becomes available. Other data, namely postal delivery data, is used when building data is suspect or not available. This program uses a best data at the best time approach. This paper outlines system development and the considerations leading to specific decisions that make the system useful, timely, and comprehensive.