Population is the currency with which cities operate. State and Federal entitlement grants are keyed to the population (not the number of households) in a city. Local zoning decisions are based on the city's best estimate of future population. A city is said to be "growing" if the population is greater this year than last year; a city is "declining" if it loses population. Because of the principle of "one person, one vote," population size is linked to political power. In order to project demand for the city's services, a manager must estimate the number of people who will be making that demand.
It is difficult, however, to obtain an actual count of the population at any given time. People move in and out of cities, children are born and people die. The Federal government conducts a national census of the population every ten years, but the results are not published for individual cities until two years later. It is very expensive to commission a special census to count the population for any of the intervening years. Further, even a very accurate count of current population will not tell you how to estimate future population and the demands it will make on land and services in the city.
Population estimation and population projection are among the most common of urban analytical tools. Estimating current population, based on past trends and a recent census, is a fairly quick, fairly inexpensive way to provide information for current planning. It is less accurate than an actual census, but it usually comes fairly close. Population projection (estimating future population based on past trends and a recent census) is the only way to provide estimates of the expected size and needs of the city.
© 1996 A.J.Filipovitch
Revised 11 March 2005