Graphical Skills » Cross-sections and Dispersion Graphs

What you'll learn this session

Study time: 30 minutes

How to read and interpret cross-sections of landscapes
How to create accurate cross-section profiles from contour maps
Understanding dispersion graphs and scatter plots
How to plot and analyse dispersion graphs
Calculating and interpreting correlation in geographical data
Practical applications of these graphical skills in geography fieldwork

Cross-Sections in Geography

Cross-sections are like slicing through a landscape to see what it looks like from the side. They help us visualise the shape of the land along a specific line, showing hills, valleys and other features that might not be obvious from a flat map.

Key Definitions:

Cross-section: A side-view diagram showing the shape of the land surface along a chosen line.
Vertical exaggeration: When the vertical scale is larger than the horizontal scale to emphasise relief features.
Contour lines: Lines on a map connecting points of equal height above sea level.

📊 Reading Cross-Sections

Cross-sections show you the profile of the land between two points. The horizontal axis represents distance, while the vertical axis shows elevation. This helps you visualise features like:

Steep slopes (contour lines close together)
Gentle slopes (contour lines far apart)
Valleys (V-shaped contour patterns)
Hills and mountains (circular contour patterns)

📝 Creating Cross-Sections

To create a cross-section:

Draw a straight line on your map where you want the cross-section
Place a piece of paper along this line
Mark where each contour line crosses your paper
Note the height of each contour line
Plot these heights on graph paper
Connect the points with a smooth line

Practical Cross-Section Skills

When drawing cross-sections, accuracy is key. The vertical and horizontal scales need to be clearly labelled and you should include a title that states the locations at each end of your cross-section.

Common Mistakes to Avoid

Forgetting to label axes
Using inconsistent scales
Drawing straight lines between points instead of smooth curves
Not accounting for vertical exaggeration
Missing contour lines when marking your paper

Interpreting Landforms from Cross-Sections

Different landforms have distinctive cross-section profiles that can help you identify them:

⛰ V-Shaped Valleys

Formed by river erosion, these have a distinctive V shape in cross-section. The steepness of the V indicates the stage of the river, with steeper Vs in the upper course.

🏔 U-Shaped Valleys

Created by glacial erosion, these have a flat bottom and steep sides forming a U shape. They're typically wider and deeper than V-shaped valleys.

🌋 Coastal Features

Cross-sections can reveal features like cliffs, wave-cut platforms and beaches. The gradient changes help identify different coastal processes.

Dispersion Graphs in Geography

Dispersion graphs (also called scatter plots) show the relationship between two variables. They're incredibly useful in geography for exploring how different factors might be connected.

Key Definitions:

Dispersion graph: A graph showing the relationship between two variables as a pattern of points.
Correlation: The statistical relationship between two variables.
Positive correlation: When one variable increases as the other increases.
Negative correlation: When one variable increases as the other decreases.
No correlation: When there's no clear relationship between the variables.

📈 Creating Dispersion Graphs

To create a dispersion graph:

Choose two variables you want to compare
Draw x and y axes and label them with the variables
Plot each pair of data as a point on the graph
Look for patterns in the distribution of points
Draw a line of best fit if there appears to be a correlation

🔍 Interpreting Patterns

The pattern of points tells you about the relationship:

Points forming a line from bottom-left to top-right show positive correlation
Points forming a line from top-left to bottom-right show negative correlation
Points scattered randomly show no correlation
Points forming a curve suggest a non-linear relationship

Analysing Correlation in Geography

In geography, we often want to know if two factors are related. For example, is there a relationship between a country's GDP and its carbon emissions? Dispersion graphs help us visualise these relationships.

👍 Positive Correlation

As one variable increases, the other also increases. Example: temperature and ice cream sales. The points trend upward from left to right.

👎 Negative Correlation

As one variable increases, the other decreases. Example: distance from the CBD and property prices. The points trend downward from left to right.

😶 No Correlation

No clear relationship between variables. Example: shoe size and exam results. The points show no clear pattern.

Case Study Focus: River Fieldwork

Students collected data from the River Wye in Derbyshire to investigate how river characteristics change downstream. They measured:

Distance from source (km)
River width (m)
River depth (cm)
Velocity (m/s)
Sediment size (mm)

Using dispersion graphs, they found:

Positive correlation between distance from source and river width/depth
Negative correlation between distance from source and sediment size
Positive correlation between velocity and distance (though with some anomalies)

This supported the Bradshaw Model of river characteristics changing predictably downstream.

Practical Applications in Geography

Both cross-sections and dispersion graphs are essential tools for geographical investigation and fieldwork.

When to Use Each Graphical Technique

🗺 Cross-Sections

Best used for:

Studying physical landscapes and relief
Understanding the shape of river valleys
Examining coastal features
Analysing urban transects (e.g., building height changes across a city)
Planning routes with minimal elevation change

📊 Dispersion Graphs

Best used for:

Investigating relationships between two variables
Testing geographical theories and models
Analysing development indicators
Studying climate data relationships
Examining spatial patterns (e.g., distance decay)

Exam Tips for Graphical Skills

In your iGCSE Geography exam, you might be asked to interpret or create cross-sections and dispersion graphs. Here are some tips:

✅ Cross-Section Tips

Always label both axes clearly with units
Include a title that states the start and end points
Draw smooth curves, not angular lines
Note any significant features (e.g., valleys, hills)
Be aware of vertical exaggeration and mention it if present

✅ Dispersion Graph Tips

Plot points accurately
Label axes with variables and units
Add a line of best fit if there's a correlation
Describe the correlation type in your answer
Identify and explain any anomalies
Remember correlation doesn't always mean causation

Remember!

Graphical skills are practical tools that help geographers make sense of complex data and landscapes. They allow us to:

Visualise what we can't easily see
Test geographical theories
Identify patterns and relationships
Make predictions based on trends
Communicate findings clearly

Practice these skills regularly with real geographical data to build your confidence!

🧠 Test Your Knowledge!