Graphics in Documents
Using Graphics to Think Preparing the graphics first helps you get started and sets out the framework of your written product
Graphical Display and Scientific Inquiry • “ . . .the way in which we present the data determines what can be seen in the data.” • Valiela, Doing Science, p. 183 • Choice of graphical display can reveal new relationships among data. • representing the data differently can lead to new findings
In 1854, Dr. John Snow made a map of deaths from the cholera epidemicin London. Example: Spatial representation of data Previously, data on deaths had been displayed chronologically. Tufte, Visual Explanations, 1997
Work House Brewery
Graphical Display • Snow took data normally displayed chronologically (x # of deaths each day throughout the epidemic) and graphed it spatially, • Spatial display convinced the authorities to shut down the Broad St. pump. From that moment, cholera seriously understood to be linked to bad water.
Lessons • Map makes quantitative comparisons visible and locates them spatially. • Map is appropriate context for showing cause and effect. • Time series chart not as effective. • Thinking about howbest to display the data will help you establish useful relationships among the data.
Graphics in Written Documents: Two Important Questions • When are graphics appropriate? • What can information display do that words alone cannot? • What makes a good graphic? • Are there relevant principles of design? • See works of William S. Cleveland and Edward R. Tufte
When are graphics appropriate? • To show complex data in a simplified form • show a lot of data in one place • To emphasize relationship better than can words alone • To help the reader remember • To allow parallel processing of information (visual and verbal)
Deciding How to Present Data • William Cleveland studied how accurately readers evaluate graphical cues. Rank of cues from most to least accurate perception: • Position along an axis • Length • Angle or slope • Area • Volume • Color and shade • Use cues that are ranked as high as possible. William Cleveland, The Elements of Graphing Data, 1994
Principles of Information Display • Read the works of Edward Tufte. • The Visual Display of Quantitative Information, 1983 • Envisioning Information, 1990 • Visual Explanations, 1997 • Tufte analyzes visuals displays of data to see which ones help the reader/viewer think through the problem or understand the results. • See article on PowerPoint in Reference list Link
Charles J. Minard’s 1861 graphic depicts Napoleon’s Russian Campaign of 1812 (Tufte, Visual Display)
Tufte calls Minard’s graphic “possibly the best ever constructed.” • Six variables are plotted: • size of army • location (latitude) • location (longitude) • direction • temperature • time (dates)
Column Position (X) 0 cm Air Sampling Points Bioreactor Packing 25 cm 50 cm 75 cm 100 cm (Air Outlet) Contaminated Air Inlet Figure 5.2. Schematic of the experimental bioreactor
Principles of Design • Keep every graphic as simple and uncluttered as the complexity of your data allows. • Beware the default parameters in Excel!
Guidelines for Labeling • Labels are a frame . . . of reference, of orientation. • Label each graphic clearly with a figure or table number and a title. • Place the figure number and title beneath a figure (graph, chart, etc.). • Place the table number and title above a table.
Correct Placement of Figure Title Figure 3. Relationship between density and temperature of air at standard atmospheric pressure. Source of data: Engineering Fluid Mechanics, 2001
Correct Placement of Table Title Table 2: Example of Table with Modified Parameters
More Labeling Guidelines • Label both axes. These labels are NOT optional. • Create a title (or a title and a caption) that draws attention to significant aspects of the graphic. • Give significant details either on the figure itself or in parentheses (or smaller type) after the title/caption. • Significant details could be experimental details (such as time of day readings taken) or source information.
Integrate graphics with your text. • In the body of the document, make sure you do the following: • Describe everything graphed. For tables, explain column headings, at least. • Draw attention to important features of data. Try to include them in title too. • Describe conclusions drawn from the data. What’s significant about those data or findings? • Place graphic close to its discussion.
Coefficient of Thermal Expansion/Shrinkage A low coefficient of thermal expansion indicates that the material will have minimal change in length given temperature fluctuations. Thermal coefficients for the patching materials are summarized in Table 4; as can be seen, FRP overlay has the lowest. Table 4. Coefficients of Thermal Expansion/Shrinkage for Patching Materials
Captions integrate graphics with text. • Cleveland advocates using captions and says they should make three contributions to understanding: • Describe everything graphed or illustrated • Draw attention to important features of data • Describe conclusions drawn from the data. • Captions are not conventional in many fields. • At least make title more than “X vs Y.”
Figure 2. Destruction of Organic Contaminants by Phytodegradation Enzymes in plant roots break down (degrade) organic contaminants. The fragments are incorporated into new plant material.
Figure 2. United States Facilities with No. 2 Emissions Source: Environmental Protection Agency, 2000, www.epa.gov/airs/mapview.htm
Correct Labeling: Cite source of data Figure 3. Relationship between density and temperature of air at standard atmospheric pressure. Source of data: Crowe, et al. Engineering Fluid Mechanics, 2001