Presented is one of a series of reports introducing public agencies and other interested parties to the capabilities of policy analysis techniques. This publication focuses upon the role of population estimation and projection in regional analysis. The first section examines population estimation methods used by the U.S. Bureau of the Census and the California State Department of Finance, while the second section deals with age structure and its impact on demand for public services. The final section uses Santa Barbara County, California, as an example to illustrate how a local analyst can use a computer program to develop population forecasts and future age distributions. Included in the appendix is the entire computer program, written in FORTRAN IV. This tool can improve local population projections and may be used by local officials in making policy decisions. (Author/WB)