© SSER Ltd. How Science Works Principles of Graph Drawing

Most data can be displayed in a variety of graphs. The Use of Graphs It is not easy to see patterns just by looking at tables of data. This is when a graph can help to show the hidden pattern… Therefore, it is vital that the choice of graph is appropriate and that the graph is drawn correctly. Some forms of graph are inappropriate for the data.

Labelling Axes The x-axis is the horizontal axis. Label both axes fully and give the units. (Remember, “x is a cross”). The y-axis is the vertical axis. Give the graph a title saying what it shows, e.g...

Labelling Axes The x-axis is the horizontal axis. Label both axes fully and give the units. (Remember, “x is a cross”). The y-axis is the vertical axis. Give the graph a title saying what it shows, e.g...

Plotting Points & Drawing Lines Use a sharp pencil to draw lines and plot ‘points’. Points should be plotted as a cross ‘x’. Use a ruler to draw straight lines and axes. If using software to draw graphs, avoid over-use of 3-d options – clear communication is the most important consideration. If two sets of data are plotted on the same graph, use different coloured lines or different symbols. Always include a key.

Plotting Points & Drawing Lines Use a sharp pencil to draw lines and plot ‘points’. Points should be plotted as a cross ‘x’. Use a ruler to draw straight lines and axes. If using software to draw graphs, avoid over-use of 3-d options – clear communication is the most important consideration. If two sets of data are plotted on the same graph, use different coloured lines or different symbols. Always include a key.

Choosing Appropriate Scales You do not always have to start the x-axis or y-axis at zero. You must also select a scale so that the graph takes up most of the allocated space and shows the trends most effectively. Look at this graph. What is wrong?

The graph has an inappropriate y-axis scale, which does not show the trend well. You do not always have to start the x-axis or y-axis at zero. You must also select a scale so that the graph takes up most of the allocated space and shows the trends most effectively. Look at this graph. What is wrong? Choosing Appropriate Scales

The upper and lower limits of the scales on both axes should be sufficient to plot all the known data. Choosing Appropriate Scales Look at this table of data, then point the cursor to select which scale you would use for the speed axis. You may be required to extend the line beyond the known data, in which case the scale should be sufficient to allow for this.

The upper and lower limits of the scales on both axes should be sufficient to plot all the known data. Choosing Appropriate Scales You may be required to extend the line beyond the known data, in which case the scale should be sufficient to allow for this. Look at this table of data, then point the cursor to select which scale you would use for the speed axis.

The x-axis is normally used to plot the independent variable and the y-axis is normally used to plot the dependent variable. Dependent & Independent Variables

The temperature depends upon when it is measured; time does not depend upon the temperature. Dependent & Independent Variables dependent independent Temperature is therefore the variable. Time is the variable. The x-axis is normally used to plot the independent variable and the y-axis is normally used to plot the dependent variable.

What’s Wrong with These Graphs? Look at the following graphs. Select the error that has been made from the choices provided.

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