MalesMales are drawn on the left. Each bar is one age group.
FemalesFemales are drawn on the right. Each bar is one age group.
Age groupsThe upright scale, youngest group at the bottom.
PopulationThe level scale: a longer bar means more people.
PrereproductiveAges 0 to 14. Too young to have children yet.
ReproductiveAges 15 to 44. The band old enough to have children.
PostreproductiveAges 45 and older. Past the ages of having children.
Four shapes 4
Rapid growthA wide base: many young people, so the population grows fast.
Slow growthThe base is a little wider than the middle.
Zero growthSides close to upright: about as many young as middle-aged.
Negative growthA base narrower than the middle: the population shrinks.
How this list was compiled: Every name checked on 2026-10-03 in at least two of these. (1) Wikipedia, Population pyramid, https://en.wikipedia.org/wiki/Population_pyramid (males to the left, females to the right; the population on the level axis and the age groups on the upright axis; expansive, stationary and constrictive pyramids). (2) G. Tyler Miller, Essentials of Ecology (2004), section Population Age Structure, https://archive.org/details/essentialsofecol0000mill (age structure diagrams for rapid, slow, zero and negative growth; ages 0 to 14, 15 to 44 and 45 and older). (3) Russell, Hertz, McMillan and others, Biology: Exploring the Diversity of Life, volume 2 (2016), https://archive.org/details/isbn_9780176598792 (prereproductive, reproductive and postreproductive; male and female; rapid, zero and negative growth; a broad base with rapid growth). (4) Hassenzahl, Hager and Berg, Visualizing Environmental Science (2013), https://archive.org/details/visualizingenvir0000hass (prereproductive 0 to 14 years, reproductive 15 to 44, postreproductive 45 and older; rapid and slow growth). The three books were read by full-text search on the Internet Archive. Licence: own work
The drawing: Drawn for this site on 2026-10-03 by a script from the numbers in this page's data. Own original chart; nothing is traced or copied. Licence: own work
How it works
This age structure diagram quiz names a part and you tap it. Seven are on one large diagram: its two sides, two scales and three brackets. The last four ask which small diagram shows which kind of growth.
Read the full guide
Scales and brackets that get mixed up
Age groups is the upright scale up the middle, and Population is the level scale along the bottom. Every bar below the top one is five years of age, so the brackets differ in length. The shortest, beside three bars, is prereproductive. The middle one, beside six, is reproductive. The longest, beside the top nine, is postreproductive.
Slow growth or zero growth?
These two shapes are the most alike. Two dashed lines cross the four small diagrams at the borders of the bands. Compare the three bars under the lower line with the six between the lines. In slow growth the lowest bars are still the widest; in zero growth both sets are about the same width.
Questions and answers
What are expansive, stationary and constrictive pyramids?
Other names for three of the shapes. An expansive pyramid shows rapid growth, a stationary one zero growth and a constrictive one negative growth. The quiz takes either name as a typed answer, and stable and declining count too.
Why does every age structure diagram narrow at the top?
Because death rates rise at higher ages, each older age group holds fewer people. Even in a population that is not growing, the sides stay close to upright only through the younger ages and then draw in.
Are the male and female sides always the same?
Not on a diagram of a real population. Older age groups usually hold more females than males, because women tend to live longer. The diagrams in this quiz are schematic and draw the two sides alike.
What is on the x-axis of an age structure diagram?
Population. It can be given as a number of people or as a percent of the whole population. Here it is in percent and is counted outward from zero in the middle, once for each sex. The y-axis holds the age groups.