S2 Geography | Hong Kong Population and Population Structure: Density, Dependency Ratio and Ageing

S2 Geography | Hong Kong Population and Population Structure: Density, Dependency Ratio and Ageing — Tutor Prep Guide

2026-11-15

Tutor lesson-prep guides · Junior Secondary Geography

Students see 6,818 people per square kilometre and conclude the city is crowded, without seeing why that average is meaningless. This lesson uses built-up area, age structure and negative natural increase to turn a single total into a structure.

Objectives — Students can: (1) divide population by land area to find density and explain why average density cannot measure crowding; (2) use age-group figures to calculate the dependency ratio and explain its effect on the labour force; (3) separate natural increase from net migration and explain why a population can still grow when births fall below deaths.

01 Prerequisites (3-minute check)

If any of these fails, fix it before the lesson starts.

Skill	Quick check	Pass mark
Population density	1,000 people live in 2 square kilometres. What is the density?	500 people per square kilometre
Ratios and percentages	200 elderly people per 1,000 residents is what percentage?	20%
Land use	What are the main land use types in Hong Kong?	Residential, commercial, industrial, transport, institutional and open space

02 Lesson flow (45 minutes)

Time	Stage	Tutor does	Student does
0-5 min	Start with one number	Write 7.5 million people and 1,100 square kilometres, ask for a rough density	Estimate a few thousand per square kilometre
5-17 min	Density is not crowding	Explain that about 40% of land is country park and steep slope, then divide again using built-up area	Say that average density understates real living density
17-29 min	Age structure	Use 1.5 million aged 65 or above and a 3.8 million labour force to get 20% and the dependency ratio	Get 20% and about 632 per thousand
29-37 min	Negative natural increase	Birth rate 5 per thousand against death rate 8.5 per thousand gives about minus 26,250 a year	Get minus 3.5 per thousand and note it is negative
37-42 min	Why population still moves	Ask why population need not fall when natural increase is negative	Name one-way permits and talent schemes as net migration
42-45 min	Exit check	Ask for two consequences of an ageing population	A rising dependency ratio and a shrinking labour force

03 Teaching script (read it out)

Scene 1: Population density: the average always hides the map

The point of this section is that an average hides distribution. Let students compute it first: 7.5 million divided by 1,100 square kilometres gives about 6,818 people per square kilometre, which does not look extreme next to New York or Mumbai. Then dismantle it: about 40% of Hong Kong is country park and steep slope, and the built-up area where people actually live is roughly a quarter of the territory, so the same people divided by that area push density past 20,000. A question asking whether Hong Kong is crowded cannot be answered with 6,818, because the denominator answers a different question; it has to be answered with built-up density and floor area per person. That is the moment students see that identical units do not mean identical meaning.

Ask students to say what is wrong with the denominator in 6,818 and which area should replace it

Scene 2: Age structure: a division and a policy problem at once

Do not teach age structure with a pie chart. Use three numbers: 7.5 million total, 1.5 million aged 65 or above, so 20%, and a labour force of 3.8 million. Ask what 20% means, then ask who supports whom. The dependency ratio is (young plus elderly) divided by the labour force, times 1,000; with 1.5 million elderly and about 0.9 million young against 3.8 million workers it comes to about 632 per thousand, meaning every 1,000 workers support 632 dependants. Then force students to see both directions: the numerator rises as the population ages while the denominator shrinks as the labour force falls, so the ratio deteriorates faster than either trend alone. Finish by mapping policy to the arithmetic: talent schemes and later retirement move the denominator, birth incentives move the numerator.

Ask students to name the numerator and denominator of the dependency ratio and which side one policy moves

Scene 3: Negative natural increase: two separate flows

The commonest misconception is that more deaths than births must shrink the population. Teach instead that population change equals natural increase plus net migration. Compute natural increase first: a birth rate of 5 per thousand against a death rate of 8.5 per thousand gives minus 3.5 per thousand, which on 7.5 million is about minus 26,250 people a year. Then ask why published population figures can still rise: because net migration is positive, with family reunion permits and talent schemes adding more people than natural decrease removes. The correct sentence is therefore that natural increase is negative and total change depends on migration. That frame carries straight into later S2 questions on labour supply and the speed of ageing.

Ask students to state in one sentence how natural increase and net migration each affect the total

04 Question types and worked steps

Type	Example	Steps	Answer
Density calculation	Hong Kong has about 7.5 million people over about 1,100 square kilometres. What is the population density?	(1) Population divided by area (2) 7,500,000 / 1,100 (3) keep the unit as people per square kilometre	About 6,818 people per square kilometre
Dependency ratio	1.5 million aged 65 or above, 0.9 million young, 3.8 million in the labour force. What is the dependency ratio?	(1) The numerator is dependants (2) divide by the labour force (3) multiply by 1,000	About 632 per thousand, so every 1,000 workers support 632 people
Growth decomposition	Birth rate 5 per thousand, death rate 8.5 per thousand, population 7.5 million. What is the annual natural increase?	(1) Subtract first to get minus 3.5 per thousand (2) multiply by population (3) keep the negative sign	About minus 26,250 people, a natural decrease
Discussion	How does an ageing population affect Hong Kong labour supply? Give two responses.	(1) State the falling share of workers (2) state the rising dependency ratio (3) say whether each response moves the numerator or the denominator	Fewer workers and higher costs; later retirement and talent schemes move the denominator, birth incentives move the numerator

Sanity check (teach this): Run a three-step ratio check: (1) is the numerator the dependant population rather than the total; (2) is the denominator the labour force rather than the total; (3) per thousand multiplies by 1,000 and percentage by 100, and mixing them is a factor of ten. For density, check the denominator: the whole territory gives 6,818 and the built-up area gives more than 20,000, and both are correct answers to different questions.

05 Independent practice (3 questions)

Question	Answer	What to watch
7.5 million people over 1,100 square kilometres: what density?	About 6,818 per square kilometre	Did they invert area and population?
1.5 million elderly, 0.9 million young, 3.8 million workers: dependency ratio?	About 632 per thousand	Did they divide by the total population?
Why can population rise when natural increase is negative?	Because net migration is positive	Did they keep the two flows separate?

06 Common mistakes and what to say

Mistake	Student writes	Say this
Using average density to judge crowding	Density is 6,818 per square kilometre, so Hong Kong is not crowded.	“6,818 divides by the whole territory including country parks and mountains. To answer the crowding question, divide by the built-up area instead.”
Wrong denominator for the ratio	1.5 million plus 0.9 million divided by 7.5 million gives 32%.	“The denominator is the labour force of 3.8 million, not the total. Dividing by 7.5 million counts people as supporting themselves.”
Per thousand written as a percentage	The dependency ratio is 63.2%.	“632 per thousand is 63.2%, so your value is right but the unit is wrong. The question asked for per thousand, so write 632.”
Treating negative natural increase as population decline	Births are below deaths, so the population must fall every year.	“You only counted natural increase. Population change adds net migration, and inbound movement can outweigh the natural decrease.”

07 Homework (paper, section and question numbers)

Water supply chapter, question 2 (days of storage) — More people means higher daily demand, so the same reservoirs last fewer days
Agriculture and fisheries chapter, question 1 (self-sufficiency) — Population size sets food demand, the other side of the same fraction
Transport network chapter, question 1 (trips per person) — Where people live and work sets commuting flows, used in the next chapter

08 Exit check (last 5 minutes)

Question	Answer	Decision
What is Hong Kong density, and why can it not measure crowding?	About 6,818 per square kilometre, with country parks and slopes in the denominator	Saying “very dense” without the denominator problem means the average was not understood
What share of the population is 65 or above?	About 20%, or 1.5 million	Saying 10% means the labour force share was confused
Is natural increase positive or negative, and why can population still rise?	Negative, offset by net migration	Answering only “negative” means the two flows were not separated

09 Tutor FAQ

Must students memorise the 6,818 figure?

Not exactly, but the magnitude matters: a few thousand per square kilometre, plus the line that the average includes country parks and slopes, so it cannot measure crowding.

Should the dependency ratio be per thousand or a percentage?

Both are acceptable, but if the question says per thousand, multiply by 1,000. This chapter uses per thousand throughout because population statistics do.

Can ageing be explained by the birth rate alone?

No. It is driven by falling births and longer life together, with the postwar baby boom cohort reaching retirement age, so the age structure has to be used rather than one rate.

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A TutorZone lesson-prep guide. Written by the TutorZone team; questions and lesson flow are original and are not taken from any school or publisher material.