Age Structure in AP Human Geography

Reading age structure off a population pyramid

A population pyramid stacks age groups from youngest at the bottom to oldest at the top, with males on one side and females on the other. The shape tells you the story.

• Wide base, narrow top (expansive): high birth rates and a young population. Niger, with close to half its people under 15, is the standard example. Growth is built in, because those children will reach childbearing age.
• Narrow base, wide middle or top (constrictive): low birth rates and an aging population. Japan, with nearly 30% of its people 65 or older, fits here. Without immigration, the population shrinks.
• Straight sides (stationary): birth and death rates are low and roughly balanced, so the population is stable.

This is the core of Topic 2.3: Population Composition in Unit 2: Population and Migration, which asks how geographers depict population makeup and what those pictures predict. The shape also forecasts markets. A young country needs schools, maternity care, and jobs for a coming wave of workers, while an old country needs nursing homes, pensions, and healthcare workers.

Why age structure shifts older, and the dependency ratio

Topic 2.9: Aging Populations asks you to explain why populations age and what follows. Three things drive it: birth rates, death rates, and life expectancy. Falling birth rates shrink the base of the pyramid, and longer life expectancy widens the top. Of the two, low birth rates usually do more of the work, since fewer young people automatically raises the share of old people.

The dependency ratio compares people likely too young or too old to work with people of working age: (under 15 + 65 and older) ÷ (15-64) × 100. Say a country is 30% under 15, 60% working age, and 10% elderly. That's (30 + 10) ÷ 60 × 100, or about 67 dependents per 100 working-age people. You won't have a calculator, so expect numbers that divide cleanly.

A high ratio can come from either end. A young country and an old country can both have a high dependency ratio, but the young one is short on schools and jobs, while the old one is short on workers and tax revenue. The course wants consequences in three categories:

Economic effects include labor shortages and strained pension and healthcare systems. Social effects include more family elder care and fewer young caregivers. Political effects include debates over raising the retirement age, the voting power of older citizens, pronatalist policies, and immigration to fill the workforce.

Scale, sex ratio, and the pyramid as a stimulus

Age structure varies from region to region and can be mapped at different scales, so stimulus multiple-choice questions may ask you to identify a dataset's scale or compare patterns across scales. Comparing the share of people 65+ across ASEAN member countries uses national-scale data within a regional study area, since each data point is a whole country. A map comparing all ten Canadian provinces uses subnational data across a national study area. Tracking older residents block by block in one Tokyo neighborhood is local scale.

Sex ratio gets read off the same pyramid. A big bulge of males aged roughly 20-49 with a normal-looking female side points to male labor migration, the pattern found in Gulf states like Qatar and the United Arab Emirates. A dent in one age band can mark a past war, famine, or birth-control policy.

On the FRQs, a pyramid or table of age percentages fits naturally as the data in Question 2 (one stimulus) or as one of the two sources in Question 3 (two stimuli). A top answer goes past describing the shape. It names the cause (a falling birth rate, rising life expectancy, migration) and links it to a specific consequence, like a rising dependency ratio or demand for elder care, and it often ties in another unit, such as women's education lowering fertility or an aging workforce affecting economic development.

One common mix-up is treating the pyramid and the age structure as the same thing. The pyramid is the graph; the age structure is the distribution it displays, which you can also give as plain percentages. Another is crediting aging only to longer lives, when shrinking birth rates are usually the bigger cause.