Database results:
examBoard: Cambridge
examType: IGCSE
lessonTitle: Proportional Symbols and Radial Graphs
Maps and graphs are essential tools for geographers to display data visually. Proportional symbols and radial graphs are two powerful techniques that help us understand geographical patterns and make comparisons between different places or variables.
Key Definitions:
Proportional symbols represent quantities by varying the size of a symbol (usually a circle) on a map. The larger the value, the larger the symbol. They're perfect for showing the distribution of a single variable across different locations.
Radial graphs display multiple variables for one or more locations on axes radiating from a central point. They're excellent for comparing multiple characteristics of different places or showing changes over time.
Proportional symbol maps use symbols (usually circles) whose size corresponds to the value of a particular variable at each location. They're one of the most common ways to show quantitative data on maps.
Follow these steps to create an effective proportional symbol map:
There are two main approaches to scaling symbols:
The radius of the circle is directly proportional to the data value. This is simpler to calculate but can be visually misleading since the area increases as the square of the radius.
Formula: r = k × value (where r is radius and k is a constant)
The area of the circle is proportional to the data value. This is perceptually more accurate as we tend to judge the size of symbols by their area.
Formula: A = k × value, so r = √(k × value/π)
Proportional symbol maps are commonly used to show urban population distribution. A map of global megacities might use circles of different sizes to represent population. For example, Tokyo (37 million) would have a much larger circle than London (9 million).
Using area scaling, if London's circle has a radius of 5mm, Tokyo's would have a radius of approximately 10mm (since √(37/9) ≈ 2 and 5mm × 2 = 10mm).
Radial graphs display multiple variables on axes that radiate from a central point. Each axis represents a different variable and points are plotted along each axis according to their values. These points are then connected to form a polygon.
Follow these steps to create an effective radial graph:
Radial graphs are perfect for comparing climate data across different locations. For example, a radial graph comparing London and Cairo might include axes for:
The resulting polygons would clearly show Cairo's hotter, drier climate compared to London's milder, wetter conditions.
Compare climate variables, river characteristics, soil properties, or ecosystem features across different locations.
Compare development indicators, demographic data, economic sectors, or quality of life measures between countries or regions.
Show changes in multiple variables over time, such as monthly climate data or seasonal tourism patterns.
Don't overcomplicate your visualisations. For proportional symbols, use a clean base map. For radial graphs, limit to 4-8 variables.
Use colour to enhance understanding, not just for decoration. Consider using different colours for different categories or locations.
Always include a clear title, legend and labels. For radial graphs, label each axis. For proportional symbols, include a scale.
In your iGCSE Geography exam, you might be asked to:
Practice creating both types of visualisations and be prepared to explain when each would be most appropriate to use.
Proportional symbols and radial graphs are powerful tools in a geographer's toolkit. Proportional symbol maps excel at showing the distribution and magnitude of a single variable across space, while radial graphs are perfect for comparing multiple variables between different locations or time periods.
Remember that the purpose of any visualisation is to communicate information clearly. Choose the appropriate technique based on your data and what you want to show and always ensure your visualisations are accurate, clear and well-labelled.
Log in to track your progress and mark lessons as complete!
Login NowDon't have an account? Sign up here.