Using Graphics to Make Your Point

People understand information in different ways. Some prefer text or stories. Some prefer graphics, such as charts, maps, tables, or pictures. Research shows that appropriate infographics and other visual aids can significantly improve both comprehension and retention of materials, especially more complex matters with which readers may not be familiar. Remember there were pictures drawn in caves before there was written text!

One of the benefits of graphics is to help simplify or distill data. Information on economics, employment, and air service often lends itself to graphics, since that information often shows relationships between different concepts or changes over time. Visualization aids cognition.

Guiding Principles for Graphics

Show the data clearly. Clear, detailed, and thorough labeling is needed. Be sure to include meaningful text on the graph itself (e.g., axis labels, legend, or call-out boxes). Write out explanations of the data on the graphic itself. Label important events in the data. Avoid abbreviations that will force readers to “work” to understand. Avoid orienting words vertically, if possible. Use a clear typeface that employs both upper and lower case letters.

Use simplicity in the design of the graph. A clean, uncluttered look will help readers understand. Avoid distortions, shading, perspective, and unnecessary color or decoration. Do not use three dimensions to represent something that only needs to be represented in two dimensions. Be careful with color; users with some color blindness need to be able to understand distinctions.

Use alignment on a common scale. Good graphs support accurate estimation of the quantities represented. Readers need to understand the scale used so that they can estimate the quantities displayed on the graph. Use a single linear scale whenever possible. Add gridlines to assist with accurate comparison and estimation.

Use standard forms that work. Accurate interpretation of graphs relies on a shared understanding of the definition of the graphical objects used. Standard forms for charts are discussed in the next section.

With monetary units over time, use constant dollars. In time-series displays of money, deflated and standardized units of monetary measurement are nearly always better than nominal units.

Types of Charts

There are an infinite number of charts and graphics, and many innovative graphics are highly effective means of communicating information. However, most consumers of information on air service and economic activity will expect a limited variety. Different types of charts are best for different types of data and relationships.

Bar Graphs

Bar graphs are used to compare. A bar graph uses the height of different bars to compare quantities. The bars can be shown vertically or horizontally. Bar charts showing one variable can also be used to track changes over time.

Dual-Axis Chart

A dual-axis chart (also called a multiple-axes chart) uses two axes to illustrate the relationships between two variables with different magnitudes and scales of measurement. To clarify the distinction between variables, one may be displayed with bars and the other with lines. The separate axes are needed if the scale of the variables shown varies significantly. This report uses a line/bar chart to display the changes in available seat capacity and flights over time. If both seats and flights used the same scale, the differences in the scale of the variables would make changes in the number of flights difficult if not impossible to discern. On the other hand, a challenge with dual-axis charts is that many readers have difficulty interpreting the data correctly, not immediately recognizing which axis is associated with which variable.

Change in Available Capacity and Flights at Des Moines

Time-Series Graphs

One of the most common types of graphs used in economics is called a time-series graph. A time-series graph shows how the value of a particular variable or variables has changed over some period of time. One of the variables in a time-series graph is time itself. Time is typically placed on the horizontal axis in time-series graphs. The other axis can represent any variable whose value changes over time.

Time-series graphs often use lines rather than bars to show the progression of the variable.

Pie Graphs

A pie graph (sometimes called a pie chart) is used to show how an overall total is divided into parts. A circle represents a group as a whole. The slices of this circular “pie” show the relative sizes of subgroups. In a pie graph, each slice of the pie represents a share of the total or a percentage.

Airline Market Share at Des Moines, 2019 (% of enplaned passengers)

Using Icons and Infographics to Illustrate Concepts

Using icons can also help convey information and is good a way to represent text. A good infographic includes both text and visual representations. The example shown (see “Demand for Air Transportation Helps Support More Than 10 Million U.S. Jobs”) illustrates the wide number of different jobs associated with air transport and can help readers unfamiliar with the industry understand the amount and variety of employment tied to aviation.

Using Maps as Graphic Aids

Maps are an excellent visual aid because they are a basic visual representation of geography and a unique method for conveying a great deal of information. Maps can easily display information about an issue in a succinct way. While they obviously show the location of different things, maps can also include other information (e.g., by enlarging a circle at a city, maps can show the size of the population, the number of origin and destination travelers, or comparative employment).

Personalizing the Analysis/Airport Story with Individual Examples

Personalizing an airport’s message also can help provide an audience with a new perspective on how airports work. Although many people fly regularly and see workers at the airport, they often do not fully comprehend the large numbers of employees needed for commercial aviation to operate safely and effectively. Most passengers do not grasp the total number of local employees who work for the airline or at the airport, much less the number of local businesses and workers who rely on air transportation to reach their customers or suppliers. Anecdotal information is not statistically significant, but it can be a powerful tool for helping explain a message or concept. In “The Power of Anecdote,” Janice Morse writes that

Anecdotes reveal. Anecdotes communicate the emotion and the meaning of an event. A good anecdote will have all of the characteristics of the category it represents. . .

Anecdotes make facts memorable. Anecdotes make research comprehensible; they communicate meaning and emotion, and they bring a message home. . . .

Good anecdotes enable generalization. “You can throw away the data.” Good anecdotes are really an exercise in generalization: We have generalized from the data to the anecdote; we can generalize from the anecdote about the data and generalize to other contexts and populations. . . .