Components

HOW TO GRAPH
Principles | Components


Sometimes it’s useful to break a complex object into its component parts and consider them individually. According to Klass (2012), most charts and graphs can be thought of as having three basic components:

COMPONENT #1: LABELS

The labels in charts and graphs help define the data. Charts and graphs utilize labels in a number of different places. For example, the title, axis titles, and data labels all help to define the data. So, too, do the legends defining separate data series and the notes included below the chart or graph (which are often used to indicate the source of the data). Your labels should all be both clear and precise. This is the practical expression of Klass’ graphing principle #2 (ambiguity).

COMPONENT #2: SCALES

The scales in charts and graphs help make them efficient. Thus, the proper use of scales is the practical expression of graphing principle #3 (efficiency). The scales define the range of the Y-, but also sometimes the X-, axis. Scales that are too big or too small interrupt the ability of the reader to understand the data in a timely manner because they distort the graphical elements, which are discussed below.

COMPONENT #3: GRAPHICAL ELEMENTS 

The graphical elements that represent the data include features such as the bars in bar charts, the lines in line charts, the points in scatterplots, and the ‘slices’ in pie chart. Another way to think of the graphical elements in to imagine all of the visible features enclosed by the X- and Y- axes. As with scales, the graphical elements in charts and graphs help make them efficient, which again is the practical expression of graphing principle #3 (efficiency).

[INSERT CLEARLY LABELLED EXAMPLE of a graph HERE]

Figure 1. An example of a line chart with labels to show the three main components.


A CLOSER LOOK AT EACH OF THE THREE MAIN COMPONENTS OF CHARTS AND GRAPHS

COMPONENT #1: LABELS

Titles.  In journalistic writing a chart title will sometimes state the conclusion the writer would have the reader draw from the chart.  If figure 2 were used in a Governors State University press release, the title, “Tuition and Fees Lowest at GSU” might be appropriate.  In academic writing, the title should be used to define the data series, as is shown in figure 2, without imposing a data interpretation on the reader.   Often, the units of measurement are specified at the end of the title after a colon or in parentheses in a subtitle (e.g. “constant dollars”, “% of GDP”, or “billions of US dollars”).

Axis titles. Axis titles should be brief and should not be used at all if the information merely repeats what is clear from the title and axis labels.  It would be redundant to repeat the phrase “Tuition and fees” in the Y axis of figure 2, and the X-axis title, “University”, is completely unnecessary.  If the title of the chart has the subtitle “% of GDP”,  it is not necessary to repeat either the phrase or the word “percent” in the axis title.

Data labels. Avoid using too many numbers to define the data points.  A chart that labels the value of each individual data point does not need labeling on the y axis.  If it seems necessary to label every value in a chart, consider that a table is probably a more efficient way of presenting the data.

Legends.   Legends are used in charts with more than one data series.  They should not be placed on the outside of the chart in a way than reduces the plot area, the amount of space given to represent the data.  In figure 2, the legend is placed inside the chart (although some think that detracts from the main graphical elements), it could also be placed at the bottom of the chart (where the unnecessary “university” now stands.

Data source.  Specifying the source of the data is important for proper academic citation, but it also can also give knowledgeable readers who are often familiar with common data sources important insights into the reliability and validity of the data.  For example, knowing that crime statistics come from the FBI rather than The National Criminal Victimization Survey can be a crucial bit of information.

COMPONENT #2: SCALES

Axis scale.  The value or magnitude of the main graphical elements of the chart are defined by either or both the axis scale and individual data labels.  Avoid using too many numbers to define the data points.  A chart that labels the value of each individual data point does not need labeling on the y axis.  If it seems necessary to label every value in a chart, consider that a table is probably a more efficient way of presenting the data.

COMPONENT #3: GRAPHICAL ELEMENTS 

Bars, lines, points, slices. Keep the shading of the graphical elements simple and always avoid using unnecessary 3-D effects.

Gridlines.  If used at all, gridlines should use as little ink as possible so as to not overwhelm the main graphical elements of the chart.


SOURCES

Klass, Gary M. (2012). Just Plain Data Analysis: Finding, Presenting & Interpreting Social Science Data (2nd edition). Rowman & Littlefield Publishers: New York. ISBN: 978-1-4422-1509-2 (electronic book)