Population density is the number of people divided by the area they occupy, written as people per km². The usual error comes before the division, when the wrong area is chosen.
This lesson is part of population distribution and density. The next lesson, explaining a distribution pattern, uses the numbers you get here.
What does “matched” mean?
The population figure and the area figure must describe the same place and the same boundary. Check two things before dividing: which place each number belongs to, and which unit the area uses.
Say it aloud: “These 45 000 residents live in this 150 km².” If the sentence sounds wrong, the pair is not matched.
Worked example: a district with a lake
District Bayu has 45 000 residents and a total area of 150 km². A reservoir covers 30 km² of it.
- Total area version: 45 000 ÷ 150 = 300 per km².
- Land area version: land is 150 − 30 = 120 km², so 45 000 ÷ 120 = 375 per km².
Both are correct answers to different questions. Use the area the question names, and if it names none, use the total area and say so.
The mistake that costs marks
The common slip is to divide a town’s population by the district’s area. The arithmetic looks fine, so the error is hard to spot.
Bandar Mesra has 60 000 residents. The built-up town covers 15 km². The district around it covers 200 km².
| Step | Wrong | Right |
|---|---|---|
| Area chosen | 200 km² (the district) | 15 km² (the town) |
| Working | 60 000 ÷ 200 | 60 000 ÷ 15 |
| Answer | 300 per km² | 4 000 per km² |
The wrong answer is more than thirteen times too small. It makes the town look like an ordinary rural district.
What about hectares and other units?
Convert before you divide. One km² is 100 hectares, so 2 400 hectares is 24 km².
A village belt has 9 600 residents on 2 400 hectares. Convert: 2 400 ÷ 100 = 24 km². Then 9 600 ÷ 24 = 400 per km².
Check yourself
A housing scheme has 18 000 residents. The scheme covers 600 hectares. A nearby district of 90 km² has 27 000 residents. Find the density of the scheme, and say which area you did not use.
Answer
Convert the area: 600 ÷ 100 = 6 km². Then 18 000 ÷ 6 = 3 000 per km².
The district area of 90 km² was not used, because it belongs to the district’s 27 000 residents, not the scheme’s 18 000.
What to study next
Densities become useful when you read them next to a map. Continue with reading a choropleth legend, then test the whole cluster with the density practice set.
If you want a teacher to check which area you pick and why, see online one-to-one Geography tuition.