Total population change has two sources. Natural increase comes from births and deaths, and net migration comes from people moving in and out.
This lesson is part of population growth, structure and migration. Next, read interpreting an original population pyramid to see the result in age groups.
How do you keep the two parts apart?
Use two short columns. Births and deaths go in the first, in-migrants and out-migrants in the second.
Work each column alone, then add the two answers. Never subtract deaths from a migration figure.
Worked example: a town that shrinks
Bukit Sari starts the year with 50 000 residents. It records 900 births, 400 deaths, 1 500 in-migrants and 2 100 out-migrants.
| Column | Working | Result |
|---|---|---|
| Natural change | 900 − 400 | +500 |
| Net migration | 1 500 − 2 100 | −600 |
| Total change | 500 + (−600) | −100 |
The town ends at 49 900. Rates per 1 000 of the starting population: natural increase is 500 ÷ 50 000 × 1 000 = 10 per 1 000, and net migration is −600 ÷ 50 000 × 1 000 = −12 per 1 000.
The mistake that costs marks
The common slip is to see a fall in total population and explain it with “low birth rate”. Here births exceed deaths, so natural change is positive.
- Wrong: “Bukit Sari shrank because few babies were born.”
- Right: “Bukit Sari shrank because more people moved out than moved in, which outweighed its natural increase.”
The fix is to check the sign of each column before writing the cause.
Check yourself
A district starts with 80 000 residents. It records 1 600 births, 600 deaths, 2 400 in-migrants and 800 out-migrants. Find natural change, net migration, total change and the final population. Which part contributed more of the growth?
Answer
Natural change is 1 600 − 600 = +1 000. Net migration is 2 400 − 800 = +1 600. Total change is 1 000 + 1 600 = +2 600, so the district ends at 82 600.
Migration supplied 1 600 of 2 600, which is about 62%, and natural increase supplied about 38%. Migration contributed more.
What to study next
Growth shapes the age groups in a pyramid. Continue with interpreting an original population pyramid, then try the growth and migration practice set.
If you want a teacher to check your columns on practice questions, see online one-to-one Geography tuition.