ACARA v9 CONTENT DESCRIPTION “select and construct appropriate representations, including tables, graphs, models and mathematical relationships, to organise and process data and information”
Builds on recording data with care. Once you have a careful table of numbers, the next skill is choosing how to represent it. A table keeps exact values, but a well-chosen graph can make a pattern leap off the page that the raw numbers hide.
The same data, two jobs
A table and a graph do different jobs. A table is best when you want to read an exact value, such as the rainfall in a single month. A graph is best when you want to see the whole shape at once. Choosing the right representation is not decoration: it is how you process the data so a relationship becomes clear.
Monthly rainfall in a temperate city
Average rainfall for each month of the year, in millimetres. Start with the table, then switch to a graph and watch the seasonal pattern appear.
In the table the wettest and driest months are hard to spot. As a line graph the pattern is obvious: rainfall peaks around autumn and early winter, then falls through spring. The graph reveals a relationship the column of numbers hides.
Match the graph to the question
Different questions call for different graphs. To compare separate categories, a bar chart lines them up side by side. To follow a measurement that changes in order over time, a line graph joins the points so the trend is visible. The month always goes along the bottom, because it is the variable set in order, and rainfall goes up the side, because it is what was measured.
Compare two cities side by side
Total yearly rainfall for four cities. Here the categories are separate places, so try the bar chart to compare them at a glance.
These are separate places, not a sequence in time, so a bar chart compares them best. The bars make it instant: the hills are the wettest and the desert by far the driest, a contrast that is slow to read from the numbers alone.
A graph makes the odd point stand out
One reason to graph data is that an out-of-place value, almost invisible in a column of numbers, jumps out as a point off the line. Here a city recorded its daytime high temperature on six days of a heatwave. The values rise smoothly except for one day that breaks the trend, which the graph exposes at a glance.
Read the graph: find the day that breaks the trend
Daytime high temperature recorded over six days of a heatwave. The values climb steadily except for one day that does not fit.
Click the point that does not fit the pattern of the others.
Does the graph really support the conclusion?
Choosing a graph is only half the skill. You also have to read it honestly. A graph of the monthly rainfall supports some conclusions but not others. Sort each statement by whether the rainfall data genuinely supports it, or whether it claims more than the graph can show.
Test conclusions against the rainfall graph
Use the monthly rainfall graph from earlier. Decide which conclusions the data actually supports.
Claim: The rainfall data supports the statement being judged.
The wetter months fall around autumn and early winter, not in spring.
March received more rainfall than August.
It rained on every single day in June.
The driest months sit in the second half of the year.
Next year March will be the wettest month again.
Decide whether each statement is evidence for the claim, or not.
Why this matters
Data only becomes knowledge once it is organised so people can see what it means. Knowing when to use a table, a bar chart or a line graph, and which variable goes on each axis, lets you reveal patterns and relationships clearly. Scientists, weather forecasters and engineers all rely on choosing the right representation to make sense of their measurements.
Quick self-check
1. You have monthly rainfall totals and want to spot the wettest and driest seasons quickly. The clearest representation is usually a...
2. A table is most useful when you need to...
3. For rainfall measured month by month across a year, which graph best shows the rise and fall through the seasons?
4. On a graph of rainfall against month, the months go on the horizontal axis because they are the...
5. What is the main reason to turn a data table into a graph?