Map and Fieldwork Skills » Contour lines and relief features

What you'll learn this session

Study time: 30 minutes

How to interpret contour lines on topographic maps
How to identify key relief features from contour patterns
How to calculate gradient using contour information
How to create and interpret cross-section profiles
How to apply contour knowledge in geographical fieldwork

Understanding Contour Lines

Contour lines are one of the most important features on topographic maps. They help us visualise the three-dimensional landscape on a flat, two-dimensional map. Without contour lines, we would have no way of knowing whether we're looking at mountains, valleys, or flat plains!

Key Definitions:

Contour line: A line on a map connecting points of equal elevation above sea level.
Contour interval: The vertical distance between consecutive contour lines (usually stated in the map legend).
Relief: The variation in height of the land surface, including hills, valleys and other landforms.
Spot height: A point on a map with a specific height measurement, often marked with a dot and number.

Contour Line Basics – Remember These!

Contour lines never cross each other (except in the rare case of an overhanging cliff)
Closely spaced contour lines indicate steep slopes
Widely spaced contour lines indicate gentle slopes
Contour lines form a V-shape when crossing valleys, with the V pointing uphill
Contour lines form an M-shape when crossing spurs (ridges), with the middle pointing downhill
Closed circular contours usually represent hills or depressions (look for height values)

📏 Reading Contour Values

Every fifth contour line is usually thicker (an index contour) and labelled with its elevation. To find the value of unlabelled contours:

Locate the nearest labelled contour
Identify the contour interval from the map legend
Count up or down from the labelled contour

For example, if the contour interval is 10m and a labelled contour shows 100m, the next contour up would be 110m.

📈 Calculating Gradient

Gradient shows how steep a slope is. Calculate it using:

Gradient = Vertical height difference ÷ Horizontal distance

Express it as a ratio (1:20), fraction (1/20), or percentage (5%).

Example: If you climb 50m over a horizontal distance of 500m, the gradient is:

50 ÷ 500 = 1/10 = 1:10 = 10%

Identifying Relief Features from Contour Patterns

Contour patterns create distinctive shapes that help us identify different landforms. Learning to recognise these patterns is essential for map reading and fieldwork.

⛰ Hills and Mountains

Appear as concentric closed circles or ovals. The smallest closed contour is at the summit.

The closer the contours, the steeper the slope.

Summits often have spot heights showing the exact elevation.

⛵ Valleys and Rivers

Contours form V-shapes pointing upstream (uphill).

The closer the 'V', the steeper the valley sides.

U-shaped valleys (formed by glaciers) have more rounded contour patterns.

⛺ Ridges and Spurs

Contours form M-shapes with the middle pointing downhill.

Ridges are like upside-down valleys, extending outward from higher ground.

They often separate adjacent valleys.

More Relief Features to Recognise

🌋 Slopes and Plateaus

Uniform slope: Evenly spaced contour lines
Convex slope: Contours closer at the bottom (gets steeper downhill)
Concave slope: Contours closer at the top (gets gentler downhill)
Plateau: Widely spaced or few contours on top, closely spaced around edges

🌌 Special Features

Cliff: Multiple contour lines very close together or merging
Col/Pass: A saddle-shaped dip between two higher areas (looks like an hourglass)
Depression: Closed contours with hachures (short lines) pointing inward
Escarpment: A long, steep slope with contours very close on one side

Creating and Interpreting Cross-Sections

A cross-section (or profile) shows what the landscape would look like if you sliced through it vertically, like cutting through a cake. Creating cross-sections from contour maps helps visualise the relief.

How to Draw a Cross-Section:

Draw a straight line on your map where you want the cross-section (mark it X to Y)
Place a strip of paper along this line and mark where each contour crosses it
Note the elevation of each contour crossing
On graph paper, draw horizontal (distance) and vertical (elevation) axes
Plot each contour crossing at its correct elevation
Connect the points with a smooth line to create the profile

Cross-Section Tips

When drawing cross-sections for your fieldwork:

Use a suitable vertical exaggeration (often 2× or 5×) to make relief features more visible
Label key features like summits, valleys and slopes
Include a scale for both horizontal and vertical measurements
Draw the profile line as smoothly as possible (contours only give you sample points)

Practical Applications in Fieldwork

Understanding contour lines and relief features is essential for many types of geographical fieldwork. Here's how you might apply these skills:

🌍 Planning Fieldwork

Before heading out, use contour maps to:

Identify suitable study sites (e.g., river valleys, coastal features)
Plan safe and accessible routes
Estimate walking times based on distance and gradient
Predict where certain processes might be occurring (e.g., erosion on steep slopes)
Select locations for data collection that represent different relief conditions

🔬 During Fieldwork

While in the field, contour knowledge helps you:

Navigate accurately across the landscape
Record how relief influences other geographical factors
Understand why certain features exist where they do
Sketch field sketches with accurate representations of relief
Measure gradients to correlate with other data (e.g., soil erosion, vegetation types)

Case Study: River Fieldwork and Contours

River Bradshaw Model and Contours

When studying rivers, contour patterns help identify the different stages:

Upper course: Contour lines close together, V-shapes narrow and deep
Middle course: Contour lines moderately spaced, V-shapes wider
Lower course: Contour lines widely spaced, very gentle V-shapes or almost straight

Students collecting data on river velocity, channel width, or sediment size can use contour information to explain why these variables change downstream, as the gradient (calculated from contours) is a key factor influencing river processes.

Common Mistakes and How to Avoid Them

When working with contour lines in your iGCSE Geography exams or fieldwork, watch out for these common errors:

Confusing uphill and downhill directions: Remember that V-shapes point uphill in valleys
Misreading contour intervals: Always check the map legend for the correct interval
Ignoring spot heights: These provide exact elevations and help confirm your contour readings
Drawing straight lines between contour points: Landscapes are usually smooth, not angular
Forgetting scale: A 1cm gap between contours means different horizontal distances on different scale maps

Exam Practice Tips

In your iGCSE Geography exam, you might be asked to:

Identify specific landforms from contour patterns
Calculate gradients between two points
Draw or interpret cross-sections
Describe how relief might influence human activities or natural processes
Explain how you would use contour information in fieldwork planning

Practice these skills regularly with different maps and remember to use proper geographical vocabulary when describing relief features in your answers.