There are a number of ways of representing data diagrammatically. (See also Histograms).

Scatter Graphs
These are used to compare two sets of data. A line of best fit is drawn, which should pass through as many points as possible. It should have roughly the same number of points above and below it.
The less scatter there is about the best-fit line, the stronger the relationship is between the two quantities. If the points are close to the best-fit line, we say that there is a strong correlation. If the points are loosely scattered, there is a weak correlation. There is no correlation if there is no trend in the results.

Bar Chart
A bar chart is a chart where the height of bars represents the frequency. The data is 'discrete' (discontinuous- unlike histograms where the data is continuous). The bars should be separated by small gaps.

Pie Chart
A pie chart is a circle which is divided into a number of parts.

The pie chart above shows the TV viewing figures for the following TV programmes:
Eastenders, 15 million
Casualty, 10 million
Peak Practice, 5 million
The Bill, 8 million

Total number of viewers for the four programmes is 38 million. To work out the angle that 'Eastenders' will have in the pie chart, we divide 15 by 38 and multiply by 360 (degrees). This is 142 degrees. So 142 degrees of the circle represents Eastenders. Similarly, 95 degrees of the circle is Casualty, 47 degrees is Peak Practice and the remaining 76 degrees is The Bill.