Cover lesson · Geography · Year 10 · Intermediate

Population pyramids from census data

DCF: Data and computational thinking → Data and information literacy

Name: Class: Date:

Cover teacher — you need no subject knowledge

Print: this sheet, one per pupil. All the census figures are printed below, so no computers are needed. Every pupil needs a calculator and a ruler. If you are in a computer room, the same figures are in census-2021-age-sex-cardiff-conwy.csv, and pupils can use the spreadsheet formulae given in Step 2.

Run: 5 min warm-up (raw numbers or percentages?) · 15 min Step 2, work out Conwy's twenty percentages · 15 min Step 3, draw Conwy's pyramid on the empty grid · 8 min Step 4, dependency ratios · 12 min Step 5, the written comparison.

Collect: this sheet. The figures are real: they come from the 2021 Census (ONS table TS009). Every answer is on the worked example, so you can check the calculations without a calculator of your own.

What you are doing

Every ten years the census counts everyone in Wales and England on one day. The last one was on 21 March 2021. You are going to turn the census counts for two Welsh local authorities, Cardiff (the capital city) and Conwy (a north Wales coastal county including Llandudno, Colwyn Bay and part of Eryri), into population pyramids. Then you will explain why they look so different. The Cardiff pyramid is drawn for you. You build Conwy's.

Step 1 — warm-up: numbers or percentages?

In the census, 12,527 women in Cardiff were aged 70–79. In Conwy, 7,628 were. A newspaper says: “Cardiff has far more older women than Conwy.” Cardiff's total population was 362,312 and Conwy's was 114,741. Is the newspaper being fair? Work out what percentage of each area's population those women make up, then explain.

Table 1 — Conwy, Census 2021 (total population 114,741)

Age band	Males	Females
90+	533	1,151
80–89	3,059	4,053
70–79	7,069	7,628
60–69	7,881	8,514
50–59	8,263	8,996
40–49	5,981	6,331
30–39	5,799	6,227
20–29	5,297	5,264
10–19	6,079	5,687
0–9	5,627	5,302
All ages	55,588	59,153

Table 2 — Cardiff, Census 2021 (total population 362,312), already worked out

Age band	Males	Females	Males as % of total	Females as % of total
90+	858	1,844	0.2	0.5
80–89	4,568	6,765	1.3	1.9
70–79	11,130	12,527	3.1	3.5
60–69	16,074	16,764	4.4	4.6
50–59	20,270	21,396	5.6	5.9
40–49	21,089	21,408	5.8	5.9
30–39	25,440	26,479	7.0	7.3
20–29	32,882	34,303	9.1	9.5
10–19	23,809	24,133	6.6	6.7
0–9	20,730	19,843	5.7	5.5
All ages	176,850	185,462	48.8	51.3

Source: Office for National Statistics, Census 2021, table TS009 (sex by single year of age), grouped into ten-year bands for this sheet. Percentages are of the whole population, males and females together, rounded to 1 decimal place.

Step 2 — Conwy's percentages

For every cell in Table 1: count ÷ 114,741 × 100, rounded to 1 decimal place. Divide by the whole population (114,741), not by the number of males or females, or your two halves will not match Cardiff's. Check: your male column plus your female column should add up to about 100.

Spreadsheet users: in the CSV, Conwy's males are in C13:C22 and its females in D13:D22. In F13 type =ROUND(C13/114741*100,1), in G13 type =ROUND(D13/114741*100,1), then fill both down to row 22.

Step 3 — draw Conwy's pyramid

Here is Cardiff's pyramid. Use it as your model.

Now draw Conwy's on the empty grid. Each small square is 1% wide. Males go to the left of the age labels and females to the right. Use a ruler, give it a title, and shade the male bars.

Step 4 — the dependency ratio

The dependency ratio compares people who are mostly not of working age (children aged 0–15 and people aged 65 and over) with people aged 16–64. It is worked out as:

dependency ratio = (aged 0–15 + aged 65 and over) ÷ aged 16–64 × 100

Area	Aged 0–15	Aged 16–64	Aged 65+	Dependency ratio (1 d.p.)	Aged 65+ as % of total (1 d.p.)
Cardiff	65,995	243,818	52,499
Conwy	18,378	64,995	31,368

Finish this sentence for Conwy: “For every 100 people aged 16–64 in Conwy, there are …”

Step 5 — compare and explain

(a) Describe the shape of each pyramid. Where is it widest? Quote at least two of your own percentages for each area.

(b) Cardiff's widest bars are ages 20–29. Suggest two reasons why so many people in their twenties live there. The census counted students at their term-time address, even though many were at home during the 2021 lockdown. How does that rule affect this bar?

(c) Conwy's pyramid is widest from 50 to 79. Suggest why a coastal county might attract people of this age, and name two services the council will need more of because of it.

(d) In both areas the 80–89 and 90+ bars are wider on the female side. Quote Conwy's figures and give a reason.

(e) Name two things these pyramids cannot tell you, even though the data is official and accurate. Think about why people moved, and about the fact that the census is one day every ten years.

Step by step

5 min — Step 1: work out the two percentages and decide whether the newspaper is fair.
15 min — Step 2: fill in the twenty blank percentages in Table 1. Check that the two columns add up to about 100.
15 min — Step 3: draw Conwy's pyramid with a ruler, add a title and shade the male bars.
8 min — Step 4: the two dependency ratios and the two percentages aged 65+.
12 min — Step 5: answer (a) to (e) in full sentences, quoting your own figures.

Success criteria

I can explain why areas of different sizes must be compared using percentages, not raw counts.
My percentages are correct to 1 decimal place, and each one is a share of the whole population.
My pyramid has bars drawn to scale, labelled axes, a key or shading, and a title that names the place and the year.
I can calculate a dependency ratio and say what it means in words.
I can explain the shape of each pyramid using my own figures, and say what the census data cannot tell me.

If you finish early

Work out what percentage of each area's population is aged 0–19, using the ten-year bands. Which area has the larger share of young people, and does that surprise you, given Cardiff's shape?
Sketch what you think Conwy's pyramid will look like at the 2031 census if nobody moved in or out. Which bars move up, and what happens at the bottom?
On a computer, open the ONS “How the population changed” page for your own local authority and compare its 2011 and 2021 pyramids. Write two sentences on the biggest change.