2.3 Reading graphs

Another important form of communication in STM subjects is graphs. You will now look at how graphs are used in STM subjects through the example of population growth, which is a topic you will be returning to next week.

A graph is a way of showing how one set of data varies with another set of data, and it can be used to see whether the data is likely to be related to each other. For example, a graph is useful for seeing how something changes over time. Figure 5 shows the growth in the population of human beings over time. The graph has two axes: y and x. The y-axis runs vertically and typically shows the number of what is being measured. In this case, the y axis shows the population in millions of people. The x-axis runs horizontally and here has symbols representing different time periods or names of things being compared. Here the axis shows time in years.

‘BCE’ stands for ‘Before Common Era’ and CE for ‘Common Era’, and they sometimes replace ‘BC’ and ‘AD’.

Figure 5 The population of human beings over time

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This graph shows the human population in millions (vertical axis) against the time in years (horizontal axis). The graph starts at fifteen thousand years before common era, with a very low population (close to zero on this scale). The graph is almost a straight line, sloping gently upwards, to about one thousand years in common era, by which time the population was about three hundred million. The graph then curves upwards, changing to a steeply rising straight line, so that by the year two thousand, the population is 5 thousand million.

Figure 5 The population of human beings over time