A fictional population balance with migration
Two imaginary districts are compared over one calendar year using the same boundary definitions. District A starts with 20,000 residents and records 300 births,200 deaths,800 arrivals and 500 departures. District B starts with 10,000 residents and records 150 births,100 deaths,100 arrivals and 250 departures. The figures are supplied solely for arithmetic and do not represent a current national census. A student compares arrivals alone and concludes both districts grew; another treats all net change as a birth-rate effect. The class is asked to calculate total change and a simple rate using the starting population, then discuss why those numbers do not by themselves determine classroom demand, labor supply or housing requirements without age and household information.
1. Calculate natural change, net migration and total percentage change in each district.
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A has natural change 100 and net migration 300, total+400 or 2 percent of 20,000. B has natural change 50 and net migration-150, total-100 or-1 percent of 10,000. Arrivals alone cannot determine either net migration or total change.
2. What further data would support a school-capacity decision?
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Age-specific population, household composition, school enrollment, catchment boundaries, commuting and existing capacity matter. A 2 percent total increase is not automatically a 2 percent increase in schoolchildren. The starting-population rate is the stated arithmetic convention, not every possible demographic rate.