GeographyICSE Class 8 · Representation of Geographical Features

Contours, Contour Interval, Slopes and Gradient (ICSE Class 8 Geography)

Updated 17 October 2026 · Draft, not yet fact-checked

A contour is a line on a map joining places of equal height above mean sea level. The contour interval is the constant height difference between two successive contours. Contours close together show a steep slope and contours far apart show a gentle slope. Gradient = vertical interval / horizontal equivalent, written as 1 in x, where x = horizontal equivalent / vertical interval.

Understand Contours, Contour Interval, Slopes and Gradient

1. Contour and contour interval. A contour is an imaginary line joining all points at the same height above mean sea level; on a toposheet it is printed in brown. The *contour interval* (vertical interval, VI) is the difference in height between two neighbouring contours and stays the same on one sheet. If successive lines read 100 m, 120 m and 140 m, the interval is 20 m.

2. Heights that are not contours. A *spot height* is a dot with a number giving the exact height of a point. A *bench mark* (BM) is a height cut on a permanent object such as a pillar, fixed by survey. A *triangulated height* is a point fixed by triangulation and drawn as a small triangle with its height beside it. Use these to check or complete the height shown by the contours.

3. Rules of contours.

Contours never cross one another (a rare overhanging cliff is the exception).
Each contour closes on itself, on the sheet or beyond its edge.
Close spacing means a steep slope; wide spacing means a gentle slope; equal spacing means a uniform slope.
If several contours merge into one thick line, the ground is almost vertical, as at a cliff.

4. Reading slope from spacing. Between two contours the height change is always the contour interval. If the horizontal distance is short, the ground climbs quickly (steep). If the horizontal distance is long, the ground climbs slowly (gentle). Always compare spacing on the same map, because the interval is the same everywhere on it.

5. Gradient. Gradient measures steepness as a ratio: VI / HE, expressed as 1 in x with x = HE / VI. The horizontal equivalent (HE) is the ground distance between two points, found by measuring on the map and converting with the scale. Both quantities must be in the same unit before dividing. A rise of 200 m over 2,000 m of ground gives x = 2,000 / 200 = 10, so the gradient is 1 in 10. A smaller x means a steeper slope.

6. Why slopes matter. Steep slopes are hard to farm and build on; roads and railways zigzag or use tunnels. Gentle slopes carry fields, villages and straight roads. So the contour pattern helps explain where people settle and how routes run.

Contours, Contour Interval, Slopes and Gradient: key facts

Contour interval: $V I = d i f f er e n ce b e tw ee n s u ccess i v eco n t o u r s (inm) ∣ S am e v a l u ee v er y w h er eo n o n es h ee t$
Gradient: $G r a d i e n t = V I / H E ∣ W r i tt e na s 1 in x ∣ x = H E / V I ∣ V I an d H E in t h es am e u ni t$
Ground distance: $G r o u n dd i s t an ce = ma p d i s t an ce x sc a l e d e n o mina t or ∣ O n 1 : 50, 000, 1 c m = 0.5 k m$
Slope clue: $C l oseco n t o u r s = s t ee p ∣ W i d eco n t o u r s = g e n tl e ∣ E q u a l g a p s = u ni f or m ∣ M er g e d l in es = c l i f f$

How to answer Contours, Contour Interval, Slopes and Gradient questions

For a gradient question, convert everything to metres first.

1Find VI as the difference in height between the two points (or from the interval and the number of contours crossed).
2Measure the map distance and convert it to ground distance using the scale.
3Write x = HE / VI and state the gradient as 1 in x.
4Say whether the slope is steep or gentle by comparing x with the other slope, and give the effect on land use.

Contours, Contour Interval, Slopes and Gradient in real life

The idea, met in an everyday situation. Answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Choosing a cycle route

Suppose two lanes lead from a village to the same temple 1.2 km away. Lane A rises 60 m over its length; lane B rises 24 m over 1.2 km.

Which lane is gentler, and what is its gradient? (Treat the length as the ground distance.)

Try it first, then show the solutionSolution

Gradient of A: 1,200 / 60 = 20, so 1 in 20.
Gradient of B: 1,200 / 24 = 50, so 1 in 50.
A larger x means a gentler slope.

Answer: Lane B is gentler (1 in 50 against 1 in 20).

Memory hook: Bigger number after the "1 in", softer climb.

Tricks to remember Contours, Contour Interval, Slopes and Gradient

Short memory aids. Say each one aloud once, then use it on a question the same day.

Close crowd, steep climb
Contours packed like people in a crowded lift mean the ground changes height quickly: steep.
Use it when: Slope questions.
1 in x, big x is easy
The x in a gradient tells how many metres you travel for each metre you climb, so a bigger x is a gentler slope.
Use it when: Comparing gradients.
Same units first
Convert km to m before dividing VI by HE.
Use it when: Gradient sums.

Contours, Contour Interval, Slopes and Gradient: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Contour interval · 2 marks · Short answerBoard level

Three successive contours on a toposheet are labelled 300, 350 and 400 metres. State the contour interval and say what happens to the interval elsewhere on the same sheet.

Try it first, then show the solutionSolution

Interval = 350 - 300 = 50 m (and 400 - 350 = 50 m).
The interval is constant on one sheet, so it is 50 m everywhere on it.

Answer: Contour interval 50 m, the same throughout the sheet.

Example 2: Steep or gentle · 2 marks · Short answerBoard level

On a toposheet, the 200 m and 220 m contours are 0.3 cm apart on the east side of a hill and 1.8 cm apart on the west side. Which side is steeper and why?

Try it first, then show the solutionSolution

Both pairs differ by the same 20 m of height.
The east side covers that rise in a much shorter distance, so the contours are closer.
Close contours indicate a steep slope.

Answer: The east side is steeper because its contours are closer together.

Example 3: Gradient between two points · 3 marks · Short answerHarder board level

Point A is at 340 m and point B is at 540 m on the same slope. The ground distance between them is 2.5 km. Find the gradient.

Try it first, then show the solutionSolution

VI = 540 - 340 = 200 m.
HE = 2.5 km = 2,500 m.
x = 2,500 / 200 = 12.5.
Gradient = 1 in 12.5.

Answer: Gradient is 1 in 12.5.

Example 4: Using the scale first · 4 marks · Long answerHarder board level

On a 1:50,000 map two points are 6.4 cm apart. One is at 410 m and the other at 570 m. (a) Find the ground distance. (b) Find the gradient. (c) Is the slope steep or gentle compared with a slope of 1 in 8?

Try it first, then show the solutionSolution

(a) 1 cm = 0.5 km, so 6.4 cm = 3.2 km = 3,200 m.
(b) VI = 570 - 410 = 160 m; x = 3,200 / 160 = 20; gradient 1 in 20.
(c) 1 in 20 has a larger x than 1 in 8, so it is gentler.

Answer: (a) 3.2 km (b) 1 in 20 (c) Gentler than 1 in 8.

Example 5: Which slope for a road? · 4 marks · Long answerHOTS / competency

On a 1:25,000 map the contour interval is 20 m. Slope X has contours 0.5 cm apart and slope Y has contours 2 cm apart. (a) Find the gradient of each. (b) Which is better for a straight road? (c) Why might engineers build zigzag bends on the other slope?

Try it first, then show the solutionSolution

On 1:25,000, 1 cm = 250 m on the ground.
(a) X: HE = 0.5 x 250 = 125 m; x = 125 / 20 = 6.25, gradient 1 in 6.25. Y: HE = 2 x 250 = 500 m; x = 500 / 20 = 25, gradient 1 in 25.
(b) Slope Y is gentler, so a straight road is practical there.
(c) On X the straight climb would be too steep for vehicles; bends lengthen the route and reduce the effective gradient.

Answer: (a) X 1 in 6.25, Y 1 in 25 (b) Y (c) Bends make the climb on X less steep.

Where students lose marks in Contours, Contour Interval, Slopes and Gradient

The slips examiners see most often, and what to write instead.

Mistake: Forgetting to convert units
Candidates divide metres by kilometres or by centimetres.
Wrong working
VI 200 m / HE 2.5 = 80, gradient 1 in 80
Right working
HE = 2,500 m; x = 2,500 / 200 = 12.5; gradient 1 in 12.5
Do this: Convert HE to metres before dividing.
Usually costs: 2 to 3 marks.
Mistake: Using map distance as ground distance
The scale step is skipped.
Do this: Multiply the map distance by the scale (1 cm = 0.5 km on 1:50,000) before using it.
Usually costs: 2 marks.
Mistake: Reversing steep and gentle
Wide spacing is wrongly linked to steep slopes.
Do this: Remember: close = steep, wide = gentle.
Usually costs: 1 mark.
Mistake: Writing the gradient as a decimal only
The question asks for the form 1 in x.
Do this: Write 1 in 12.5, not 0.08.
Usually costs: 1 mark.

Exam tips

Always write VI, HE and x on separate lines in a gradient answer.
State the scale conversion explicitly: "1 cm = 0.5 km".
End slope answers with a land-use comment (farming, roads, settlements) when the question asks for impact.
Colour reminder: contours are brown, water blue, vegetation green.

Practice questions on Contours, Contour Interval, Slopes and Gradient

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
Contours on a map close together indicate:
(a) a gentle slope
(b) a steep slope
(c) a flat plain
(d) a river valley
Hint
Close spacing means a quick change of height.
Answer
(b) a steep slope.
Q2 · 1 mark · Very short answerBoard level
Name the type of height mark described: "a dot with a number giving the exact height of one point on the map".
Hint
Not a contour line.
Answer
A spot height.
Q3 · 2 marks · Short answerBoard level
State any two rules about contour lines.
Hint
Think about crossing and closing.
Answer
Contours never cross each other, and each contour closes on itself, on the map or beyond its edge. (Also: close contours mean steep slopes and wide contours mean gentle slopes.)
Q4 · 3 marks · Short answerHarder board level
The vertical interval between two places is 120 m and the horizontal equivalent is 3.6 km. Find the gradient and say whether it is steeper than 1 in 40.
Hint
HE in metres first.
Answer
HE = 3,600 m; x = 3,600 / 120 = 30. Gradient is 1 in 30. Since 30 is smaller than 40, it is steeper than 1 in 40.
Q5 · 1 mark · Assertion-reasonHarder board level
Assertion (A): A gradient of 1 in 5 is steeper than a gradient of 1 in 50.
Reason (R): In 1 in x, a smaller x means that the ground rises more for the same horizontal distance.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Hint
Compare how far you walk per metre climbed.
Answer
(a) For 1 in 5 you climb 1 m in 5 m, for 1 in 50 only 1 m in 50 m, so R explains A.
Q6 · 4 marks · Case-basedHOTS / competency
A student says: "The 600 m and 650 m contours on this toposheet are 3 cm apart on the 1:50,000 map, so the gradient is 1 in 3." (a) Find the correct gradient. (b) Identify the two errors in her working. (c) State whether the slope is steep or gentle.
Hint
She forgot the scale and mixed units.
Answer
(a) Ground distance = 3 x 0.5 km = 1.5 km = 1,500 m; VI = 50 m; x = 1,500 / 50 = 30; gradient 1 in 30. (b) Error 1: she used the map distance (3 cm) as the horizontal equivalent instead of converting it with the scale to ground distance (1.5 km). Error 2: she did not take VI = 50 m into account or convert both quantities to the same unit (metres) before computing HE / VI. (c) A gradient of 1 in 30 is gentle.
Q7 · 2 marks · Short answerHarder board level
Explain why a road climbing a steep hillside often follows a zigzag path.
Hint
Think of effective gradient.
Answer
A zigzag lengthens the route, so the same rise is spread over a longer distance. This makes the gradient smaller, so vehicles can climb safely.
Q8 · 2 marks · Short answerHOTS / competency
Several contour lines meet and run together as one thick line on a toposheet. What does this show? Give one effect on land use.
Hint
Think of a cliff.
Answer
The slope is almost vertical, as at a cliff. The land cannot be farmed or built on and is a barrier to roads.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.What is a contour?Show answer
An imaginary line joining places of equal height above mean sea level.
2.What is the contour interval?Show answer
The difference in height between two successive contours; constant on one sheet.
3.Meaning of 1 in 20?Show answer
The ground rises 1 m for every 20 m of horizontal distance.
4.Which slope has widely spaced contours?Show answer
A gentle slope.
5.Colour of contours on a toposheet?Show answer
Brown.

Contours, Contour Interval, Slopes and Gradient: frequently asked questions

Do contours ever cross?

No. Only an overhanging cliff, rarely shown, is an exception.

What is the difference between a spot height and a bench mark?

A spot height is a surveyed point on the ground shown as a dot; a bench mark is a height cut on a permanent object such as a pillar or building.

Is a larger x in 1 in x steeper?

No. A larger x means a gentler slope.

Is the contour interval the same on every toposheet?

No. It is constant on one sheet, but different sheets may use different intervals; read it from the margin.