Plotting Scatter Graphs
Grade 3Setting up the axes
A scatter graph shows paired data — two measurements taken from the same subject (e.g. height and shoe size for the same person). One variable goes on the x-axis and the other on the y-axis.
If one variable is being used to predict the other, the predicting variable (called the independent variable) goes on the x-axis. If there's no obvious direction, either variable can go on either axis.
Label both axes with the variable name and its units. Choose a scale that uses most of the grid — a scale that squashes all your points into one corner makes patterns hard to see.
Plotting the points
EXAMPLE
Plot this paired data on a scatter graph: (2, 5), (3, 7), (5, 8), (6, 11), (8, 13).
Set x-axis from 0 to 9 (or 10), y-axis from 0 to 14 (or 15). For each pair, find the x-value on the horizontal axis, then move up to the y-value and mark a cross. Five crosses total. Five points correctly plotted at the given coordinates.
Common mistakes
The most common error is swapping the coordinates — plotting (5, 3) when the data says (3, 5). Always read across to x first, then up to y.
Use a cross (×) to mark each point, not a dot. Dots are easy to miss; a cross is unambiguous and easier for the examiner to check.
