Graphs
There are many different graphs. Each type shows information in a different way. Some
are very simple, others are more complex. Advantages of good graphs:
Data is presented visually
They are quick and easy to read
It is easy to compare data on the graph
It is easy to compare one graph with another
Be careful that any graph you construct that you give an accurate title (what, where,
when). This is easy marks if you can get it correct. Be aware that not all the graphs listed
below have the titles that you would be expected to have.
Bar Graphs / Column Graphs
Bar graphs can be drawn with gaps between the bars or without. They are often called
column graphs when they have gaps between the bars or when multiple data is presented
on each bar. When each piece of data on the x axis is relatively unrelated to the others
(e.g. quality of life statistics for a particular country) a column graph with gaps between
the bars is drawn. Multi-bar graphs are drawn when the same data is to be presented for
more than one area. Independent data is shown on the horizontal axis and dependent data
on the vertical axis. The labelling for bar graphs is always written directly underneath
each bar on the x axis.
Histograms
Histograms are used to plot measured continuous data which is linked or related on the x
axis. This data is classified into groups to plot onto the x axis. When plotted, the data will
sometimes form a pattern known as a normal distribution curve or a bell curve. When
drawing histograms no gaps are left between the bars and the labelling is on the line
between the bars on the x axis.
Comparative Column Graphs
Comparative column graphs are used to show two or more comparable sets of data, for
say different years or places, such as production figures of three different products for
five consecutive years.
Percentage Bar Graphs
A percentage bar graph is another type of graph that is used to show percentages.
Information like the percentage of ethnic groups in New Zealand can be shown on a
percentage bar graph. Percentage bar graphs are relatively easy to construct but it is
important to remember that they are different to ordinary bar graphs.
Pie Graphs
A pie graph is used to display percentage figures. Both pie graphs and percentage pie
graphs can be used for percentages. A pie graph differs from other graphs because it is
circular!
Climate Graphs
Climate graphs are a combination of a bar graph and a line graph. They are used to
display rainfall and temperature statistics for one area. Rainfall statistics are measured in
millimetres (mm) and are always blue and temperature in degrees Celsius (oC) and are
always red. It does not matter which side of the graph the rainfall and temperature
statistics appear, although rainfall is more commonly shown on the right.
Line Graphs
A line graph is used when the statistics to be graphed show patterns of change. Line
graphs show changes over time. Each plotted point relates directly to the point before it
and after it. They bare all related to each other. Not all the possible data is necessarily
shown on the graph.
Scatter Graphs
Scatter graphs or scatter grams are used to show the relationship between two variable
(sets of data). The relationship may be positive, as one variable increases so does the
other (for example, as a city’s population increases so do waste levels). The relationship
may be negative, as one variable increases the other decreases (for example, as
temperature increases, electricity bills decrease). Or the variables may show no
correlation (relationship) to each other (for example, the car sales and the birth rate
statistics for a town).
Triple Axes Graphs
Triple axes graphs are another variation of the basic scatter graph. They are used to
compare three variables. A common use of triple axes graphs is to show the composition
of soil. The percentages of three main soil components, sand, clay and silt can be
compared. This type of graph can be used for the percentage comparison of any three
related variables.