The U.S. Constitution requires a population census every 10 years for apportioning seats in the House of Representatives. Decennial census data are used, too, for within-state redistricting and in certain formulas for distributing more than $450 billion annually in federal funds to states and localities. Census counts also are the foundation for estimates of current population size between censuses and projections of future size. Businesses, nonprofit organizations, researchers, and all levels of government are steady consumers of decennial and other census data. The bureau's task in...