Choropleth maps (Edexcel GCSE Statistics): Revision Notes
Choropleth maps
A choropleth map is a powerful way to display how data changes across different areas using colours or shading patterns. These maps help us visualise the distribution of information geographically, making it easy to spot patterns and compare different regions at a glance.
What are choropleth maps?
Choropleth maps work by using different colours or shading to represent how data varies across different geographic areas. The darker or more intense the shading, the higher the value being represented. For example, you might see a map showing population density where darker areas represent more densely populated regions.
Every choropleth map must include a key (also called a legend) that explains what each colour or shading pattern represents. Without this key, you cannot properly interpret what the map is showing you.
Reading and interpreting choropleth maps
When you look at a choropleth map, always start by examining the key. This will tell you:
- What data is being represented
- What each colour or shading pattern means
- The range of values for each category
The key typically shows intervals, such as "0-10", "11-20", "21-30", and so on. Each interval corresponds to a different shade or pattern on the map.
To interpret the map effectively:
- Look at the overall pattern - where are the highest and lowest values?
- Compare different areas using the key as your guide
- Identify any trends or clusters in the data
- Consider what might cause the patterns you observe
Choropleth maps on grids
You can create choropleth maps using grid systems, where each square represents a specific area. This is particularly useful when working with data that covers a regular area, such as a field divided into equal sections.
When creating a grid-based choropleth map, each square in the grid is shaded according to the data value it contains. This makes it easy to see how values change across the entire area.
Worked example walkthrough
Worked Example: Creating a Choropleth Map
The problem: A field is divided into 2-metre squares, and the numbers in each square show how many flowers are found there.
Step 1: Examine the data Look at all the values to find the highest and lowest numbers. In this example, the values range from 9 to 31 flowers per square.
Step 2: Create appropriate intervals Divide the range into suitable intervals. For this data:
- 31-40 (darkest shading)
- 21-30 (medium-dark shading)
- 11-20 (medium-light shading)
- 0-10 (lightest shading)
Step 3: Apply the shading Shade each square according to which interval its value falls into. Use the key to ensure consistency.
Step 4: Interpret the results Describe what the completed map shows. In this example, "There is a higher density of flowers on the edges of the field."
Exam considerations
In your GCSE exam, choropleth maps will use different shades of grey or specific shading patterns instead of colours. This is because you cannot use colour on exam papers.
The shading typically progresses from white (lowest values) to black (highest values), with various patterns in between such as:
- No shading (white)
- Light dotted pattern
- Diagonal lines
- Cross-hatching
- Solid black
Always ensure your shading is clear and consistent with the key you create.
Creating effective keys and intervals
When you need to create your own choropleth map:
- Find the range: Identify the highest and lowest values in your data
- Choose suitable intervals: Divide the range into 3-5 groups that make sense for your data
- Make intervals equal where possible: This makes the map easier to interpret
- Create a clear key: Show each interval with its corresponding shading pattern
For example, if your data ranges from 80 to 330, you might use intervals like:
- 80-120
- 121-200
- 201-280
- 281-330
Describing distribution patterns
When asked to describe what a choropleth map shows, focus on:
Spatial patterns:
- Where are the highest/lowest values located?
- Are there any clusters or concentrations?
- Do values change gradually or suddenly between areas?
General trends:
- Is there an overall pattern (e.g., higher values in the centre, lower at edges)?
- Are there any obvious geographical influences?
- What does the distribution tell us about the underlying data?
Use specific language like "concentrated in," "distributed across," "higher density," or "clustered around" to make your descriptions precise and geographical.
Common exam tips
Critical Exam Reminders:
- Always include a clear, properly labelled key
- Use consistent shading throughout your map
- When describing patterns, refer to specific areas or regions
- Make general comments about the overall distribution
- Check that your intervals don't overlap (e.g., use 0-10, 11-20, not 0-10, 10-20)
Remember!
Key Points to Remember:
- Choropleth maps use colours or shading to show how data varies across different geographic areas
- Every choropleth map must have a key to explain what the shading represents
- In exams, you'll use different patterns and shades of grey instead of colours
- Always examine the highest and lowest values before creating intervals for your key
- When describing patterns, make specific references to where high and low values are located