Cartographic Skills » Choropleth and Distribution Maps

What you'll learn this session

Study time: 30 minutes

What choropleth and distribution maps are and how they differ
How to read, interpret and create choropleth maps
How to effectively use distribution maps to show spatial patterns
The advantages and limitations of both mapping techniques
Real-world applications of these cartographic skills

Introduction to Cartographic Skills: Choropleth and Distribution Maps

Maps are essential tools for geographers to display spatial information. Two of the most common types you'll need to understand for your iGCSE Geography are choropleth maps and distribution maps. These mapping techniques help us visualise data across different areas and identify patterns that might not be obvious from raw numbers.

Key Definitions:

Cartography: The science and practice of making maps.
Choropleth Map: A thematic map where areas are shaded according to statistical values.
Distribution Map: A map that shows the spatial arrangement of features using symbols.
Spatial Pattern: The arrangement of features across geographic space.

🗺 Choropleth Maps

Choropleth maps use different colours or shading patterns to represent data values across pre-defined areas like countries, counties, or census districts. The intensity of colour typically corresponds to the value of the data being mapped.

📌 Distribution Maps

Distribution maps use symbols (dots, icons, or other markers) to show where specific features or phenomena are located. They help visualise how things are spread out across an area without being limited by administrative boundaries.

Understanding Choropleth Maps

Choropleth maps are perfect for showing how values vary across different regions. They're commonly used to display population density, income levels, election results and other statistical data that can be linked to specific areas.

Creating Effective Choropleth Maps

To create a useful choropleth map, you need to follow these key principles:

📊 Data Classification

Group your data into categories (usually 4-7) that make sense. Common methods include equal intervals, quantiles, or natural breaks.

🎨 Colour Selection

Choose a logical colour scheme. Sequential schemes (light to dark) work well for data that progresses from low to high values.

📄 Legend

Always include a clear legend that explains what each colour or shade represents in your data classification.

Real-World Example: UK Population Density

A choropleth map of UK population density typically shows darker colours in urban areas like London, Manchester and Birmingham, with lighter colours in rural areas like the Scottish Highlands. This instantly communicates which areas are densely populated without needing to read specific numbers.

Advantages of Choropleth Maps

Easy to read: They provide a quick visual summary of data across regions.
Pattern recognition: They help identify clusters, trends and outliers.
Familiar boundaries: Using known administrative areas makes the data easier to relate to.
Quantitative: They can display precise numerical data.

Limitations of Choropleth Maps

Ecological fallacy: The assumption that everyone in an area shares the characteristics shown by the average.
Boundary issues: Data is tied to artificial boundaries that may not reflect natural patterns.
Area distortion: Larger areas appear more prominent even if they're less significant.
Hidden variations: Internal variations within each area are not shown.

Understanding Distribution Maps

Distribution maps show the location of features using symbols. They're excellent for displaying where things are located without being constrained by administrative boundaries.

Creating Effective Distribution Maps

To make a good distribution map, consider these important elements:

🗂 Symbol Choice

Select appropriate symbols that relate to what you're mapping. Use different shapes, sizes, or colours to represent different features.

📐 Density Control

Ensure symbols don't overlap too much. If an area has many features, consider using a dot density approach where one dot represents multiple occurrences.

🔍 Scale Consideration

Make sure your symbols are proportional to the importance of what they represent and appropriate for the map scale.

Case Study: UK Flood Risk Distribution

A distribution map showing flood risk in the UK might use blue dots of varying sizes to indicate areas that have experienced flooding, with larger dots representing more severe events. This approach shows the actual locations affected rather than just administrative areas, giving a more accurate picture of where flooding occurs.

Advantages of Distribution Maps

Precise locations: They show exactly where features are located.
Not limited by boundaries: They display natural patterns that may cross administrative borders.
Visual density: Areas with many symbols appear denser, creating a visual representation of concentration.
Flexibility: They can show multiple variables using different symbols.

Limitations of Distribution Maps

Symbol overlap: In areas with many features, symbols may become crowded and difficult to distinguish.
Generalisation: The exact location may be slightly adjusted for clarity.
Subjective interpretation: The visual impact depends on symbol size and design choices.
Less quantitative: They're better at showing where things are than precise values.

Comparing Choropleth and Distribution Maps

✅ When to Use Choropleth Maps

Use choropleth maps when:

Your data is linked to specific administrative areas
You want to show variations in rates or percentages
You need to compare values across different regions
Example: Mapping unemployment rates by county

✅ When to Use Distribution Maps

Use distribution maps when:

You want to show the actual locations of features
Your data isn't tied to administrative boundaries
You need to show patterns of concentration
Example: Mapping the locations of fast food restaurants

Practical Tips for Map Interpretation

When examining any map in your iGCSE Geography exam, follow these steps:

Check the title and legend: Understand what the map is showing and what the colours or symbols represent.
Look for patterns: Identify areas of high and low values or concentrations.
Consider the context: Think about why these patterns might exist (physical features, historical factors, economic conditions).
Note anomalies: Identify any areas that don't fit the overall pattern and consider why.
Make connections: Link what you see to other geographical knowledge and concepts.

Exam Tip: Map Skills

In your iGCSE Geography exam, you might be asked to interpret maps, describe patterns, or suggest reasons for distributions. Remember to use specific place names and data from the map to support your answers. Don't just say "it's higher in the north" – specify which regions and, if possible, include values from the legend.

Creating Your Own Maps

For your coursework or classroom activities, you might need to create your own choropleth or distribution maps. Here are some simplified steps:

Creating a Simple Choropleth Map

Collect data for each area you want to map.
Decide on your data categories (usually 4-6 categories works well).
Choose a colour scheme that makes sense for your data (e.g., light to dark blues for rainfall).
Draw your base map with clear boundaries.
Shade each area according to your colour scheme.
Add a title, legend, scale and north arrow.
Include a brief explanation of what the map shows.

Creating a Simple Distribution Map

Collect location data for the features you want to map.
Choose appropriate symbols that relate to your features.
Draw your base map with key reference points.
Plot your symbols in the correct locations.
Add a title, legend, scale and north arrow.
Include a brief explanation of what the map shows.

Digital Mapping Tools

While hand-drawn maps are valuable for learning, there are many digital tools that can help you create professional-looking maps:

Google My Maps: A free tool for creating simple maps
QGIS: A free, open-source GIS software for more advanced mapping
ArcGIS Online: A web-based mapping platform (some schools have access)

Summary: Key Points to Remember

Choropleth maps use shading to show how values vary across defined areas.
Distribution maps use symbols to show where specific features are located.
Both map types have specific advantages and limitations.
Choose the appropriate map type based on your data and what you want to communicate.
Always include essential map elements: title, legend, scale and north arrow.
Practice interpreting patterns and anomalies in maps for exam success.

🧠 Test Your Knowledge!