Bar, column, line, climatic and proportional graphs

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Introduction

Writing down information into a report is not always the best way to express information. Geographers often use graphs because they are a simple, yet effective, way of showing statistical data. It is important for students to be familiar with a variety of graphs, since each one is best suited to represent certain types of information. This chapter shows students how to interpret and construct bar, column, line, climatic and proportional graphs.

Bar graphs and column graphs

Bar graphs and column graphs are relatively similar. They both consist of rectangular bars or columns which are proportional, in length, to the frequency or amount being represented. This makes bar and column graphs useful for showing comparisons between data.

Like most graphs, bar and column graphs both have a horizontal and vertical axis. Bar and column graphs also use the graphing convention which requires that the scale (number line) always increases in order and by the same amount (Eg 5, 10, 15 or 1, 2, 3). The scale of a bar graph is always placed on the horizontal axis and information is shown using horizontal (left to right) columns. When constructing a bar graph, it is a convention for the bars to be drawn in order of length (longest at the top to shortest at the bottom).

The main difference between bar and column graphs is that column graphs use vertical (up and down) columns. The scale of a column graph is found on the vertical axis. On a column graph, the columns do not need to be arranged according to height. It is not uncommon for the columns to be structured in a chronological order (according to time), occurring from left to right.

When constructing bar and column graphs it is often best to start by drawing the horizontal and vertical axis. The next step involves labelling and marking an appropriate scale, including the unit of measurement, on the horizontal (for a bar graph) or vertical (for a column graph) axis. The remaining axis also needs to be labelled and divisions need to be marked. It is important for every graph to also include a title and a source (where the information is from).

Below is an example of a bar graph (Graph 1) and a column graph (Graph 2).

Graph 1. Bar graph. Source: Australian Bureau of Statistics, March 2006.

Graph 2. Column graph. Source: Australian Bureau of Statistics, March 2006.

Line graphs

Line graphs have thin lines which often show the trend or change of something (or the differences between several things) over time. Line graphs are oriented and structured in a similar way to column graphs. The scale, which occurs in ascending order and by equal amounts, of a line graph is located on the vertical axis. The data on the horizontal axis of a line graph also must appear from left to right.

When constructing a line graph, it is easier to plot the points on the graph then connect each point with a single line. Line graphs need to be correctly labelled like all other graphs. They need to have a title and source, and both axes (including the units of measurement) need to be marked appropriately.

Below is an example of a line graph (Graph 3).

Graph 3: Line graph. Source: Australian Bureau of Statistics, March 2006.

Climatic graphs

A climatic graph shows the climate (temperature and precipitation) of a particular area over the period of a year. Climatic graphs show this data by using a line graph to represent the monthly temperatures and a column graph to show the monthly precipitation.

To construct a climatic graph, the horizontal axis needs to be divided into twelve, equal spaces (one for each month). The scale on the left vertical axis needs to be appropriately divided and marked to display the temperature data. The scale on the right vertical axis needs to be divided and marked to represent the precipitation data.

Precipitation is recorded as a bar graph. The temperature needs to be recorded in the form of a line graph. Since each column represents a month, it is important that the temperature is plotted in the middle of the vertical gridlines. This will prevent any confusion about which month the temperature corresponds with.

Below is an example of a climatic chart (Graph 4).

Table 1: Table of average temperatures and precipitation of Albany, WA (Altitude: 68m). Source: Longman Atlas, 1999.

 Month Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec Av. Temp (oc) 19.5 19.5 18.5 17 14.5 12.5 11.5 11.5 12.5 14 16 17.5 Av.Precip(mm) 28 25 29 66 102 104 126 104 81 80 46 24

Graph 4. Climatic graph. Source: Longman Atlas, 1999.

Proportional graphs

Rather than being plotted on a horizontal and vertical axis like most other graphs, proportional graphs feature a series of images or symbols (often circles). The sizes or areas of these images are constructed in proportion to the amount, degree or frequency of the data which is being represented. Being able to directly compare the sizes of the images makes the data easily comprehendible.

Below is an example of a proportional graph (Graph 5).

Graph 5. Proportionate circles. Source: Essential Atlas of Physical Geography, 2003.

Comparison in the sizes of U.S. lakes

Sometimes pie charts are combined with proportional circles, to show additional information. An example of this can be seen below. Note that the pie graph of Australia is approximately five times larger than that of New Zealand. This reflects the fact that Australia's population is five times larger than New Zealand's population.

For more information on pie charts refer to Topic 4, Chapter 3: Pie charts.

Graph 6a.
Proportional pie graph
Age Structure in Australia (Total population: 20 264 082)
Source: The World Factbook July, 2006.

Age structure in Australia

Graph 6b.
Age Structure in New Zealand (Total population: 4 076 140)
Source: The World Factbook July, 2006.

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1. What sort of graphs use images which are sized in proportion with the amount (frequency) of data that they are representing?

 Frequency graphs Representational graphs Proportionate graphs Amount graphs

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