1.7 How to draw graphs in Science
Presenting data graphically
Line Graphs
Line graphs are used when:
- The relationship between the dependent and independent variables is continuous.
- Both dependent and independent variables are measured in numbers.
Features of line graphs:
- An appropriate scale is used for each axis so that the plotted points use most of the
axis/space (work out the range of the data and the highest and lowest points). - The scale must remain the SAME along the entire axis and use easy intervals such as
10’s, 20’s, 50’s, and not intervals such as 7’s, 14’s, etc, which make it difficult to read
information off the graph. - Each axis must be labelled with what is shown on the axis and must include the
appropriate units in brackets, e.g. Temperature (◦C), Time (days), Height (cm). - Each point has an x and y co-ordinate and is plotted with a symbol which is big enough
to see, e.g. a cross or circle. - The points are then joined.
- With a ruler if the points lie in a straight line (see Figure 3) or you can draw a line of
best fit where the number of points are distributed fairly evenly on each side of the
line. - Freehand when the points appear to be following a curve (see Figure 4).
- DO NOT start the line at the origin unless there is a data point for 0. If there is no
reading for 0, then start the line at the first plotted point. - The graph must have a clear, descriptive title which outlines the relationship between
the dependent and independent variable. - If there is more than one set of data drawn on a graph, a different symbol must be used
for each set and a key or legend must define the symbols.
Chapter 1. Introduction to Life Sciences 15