How do geographers choose, construct and interpret graphs and statistics to represent and analyse geographical data accurately?
Select and construct appropriate graphs and statistical measures, and interpret data to identify and explain geographical patterns and relationships.
How to choose, construct and interpret the graphs and statistics used in SACE Stage 2 Geography, including population pyramids, choropleth maps, scatter graphs and measures such as the mean and percentage change, with worked technique.
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What this dot point is asking
This dot point complements map reading by focusing on the quantitative side of geography. Marks come from choosing the correct technique and quoting figures accurately, not from long writing, so practising the mechanics is essential.
Choosing the right graph
Different data calls for different graphs, and choosing well is itself an assessed skill.
- Line graphs show trends over time, such as population or rainfall.
- Bar and compound bar graphs compare categories or show composition.
- Population pyramids display age and sex structure and reveal a country's stage of development.
- Climate graphs combine a temperature line with rainfall bars.
- Scatter graphs show the relationship between two variables, with a line of best fit revealing correlation.
- Pie and proportional divided graphs show shares of a whole.
Choropleth maps shade areas by value, isoline maps join points of equal value, flow maps show movement, and proportional symbol maps size a symbol to a value. Matching the representation to the data type is the first decision in any data question.
Interpreting graphs precisely
Reading a graph well means quoting figures, not describing vaguely. Identify the overall trend, note the highest and lowest values with their figures, and pick out anomalies or turning points. For a line graph, state whether the trend rises, falls or fluctuates and by how much. For a population pyramid, link the shape to growth and structure: a wide base means rapid growth, a top-heavy shape means ageing.
Statistical measures
A small set of statistics recurs across the course.
- The mean (average), median (middle value) and mode (most common value) summarise a data set.
- The range shows the spread between the highest and lowest values.
- Percentages and rates standardise data so places of different sizes can be compared.
- Percentage change measures growth or decline over time.
Representing fieldwork data
In fieldwork, choosing how to present collected data is part of the assessment. Pedestrian or traffic counts suit bar graphs, environmental measurements along a transect suit a line graph or annotated cross-section, and survey results suit divided or compound graphs. The representation should make the pattern clear and match the inquiry question, with accurate scales, labels and titles.
Linking it together
A complete command of data skills means choosing the correct graph or thematic map for the data, constructing it accurately, calculating statistics such as percentage change and the mean, and interpreting patterns and relationships with precise figures while separating correlation from cause. These are the quantitative techniques Section 1 of the SACE Stage 2 Geography examination assesses and that fieldwork relies on.
Exam-style practice questions
Practice questions written in the style of SACE Board exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
2018 SACE sample2 marksA group of geography students collected and analysed data on the capacity and volume of ten reservoirs over two years, including the percentage of capacity full. Describe two other ways of presenting the data shown in the table.Show worked answer →
Two marks, so name two appropriate graph or display types and briefly say how each would show the reservoir data. The data is comparative and numerical across ten reservoirs and two years.
Bar graph (or compound/grouped bar graph): plot each reservoir on the x-axis with volume or percentage full on the y-axis, using paired bars for the current and previous year to compare reservoirs and show change at a glance.
Choropleth or proportional symbol map: if the reservoir locations are known, shade or size each by percentage full to show the spatial pattern of water storage.
Other acceptable answers include a scatter graph (capacity against volume) or a line graph comparing years. Markers want the display type named and matched to what the data shows, not just a list of graph names.
2019 SACE Stage 21 marksThe heights of major buildings along a transect were measured in storeys and their distance from the centre of the city was measured in metres. State the relationship between the two variables shown on the graph in Source 3.Show worked answer →
One mark for stating the relationship clearly using the correct statistical language. Read the scatter graph's trend.
The expected answer is a negative (inverse) relationship: as distance from the centre of the city increases, building height decreases. If the points cluster tightly around a downward trend line, you can add that it is a strong negative relationship.
Use precise wording - "negative correlation" or "as one variable increases, the other decreases" - rather than a vague comment such as "they go down". Naming the direction of the relationship is what earns the mark.