Chapter Five: Graphics
Chapter Five: Graphics
Is a picture really worth a thousand words? It depends. What about a graphic such as this (Figure 1)?
Figure 1: Pie chart showing percentages of majors declared by freshmen
I can sum this up in a sentence: "In 2006, 75% of freshmen declared an engineering major, while 20% declared food service as their major, and 5% chose animal husbandry." Not exactly 1,000 words; in fact, not much over 20. It probably was not even worth my effort creating this graphic in Excel, since it presented so little information. Now, what about this image (Figure 2)?
Figure 2: Two climbers bouldering
This photograph captures a great deal more information. If I were going to explain all of the information it encodes, I would have to describe how I was laughing because my friend Cynthia made a joke about being nervous, how I was having a hard time spotting footholds for her because of the sun in my eyes, how it was an unusually warm day for November, etc. I might get close to 1,000 words. Certainly, if this photograph had depicted the getaway of an armed robber or the signing of an important treaty, we might need much more than 1,000 words. Finally, consider this graphic (Figure 3):
Figure 3: fever chart from http://www.caltriplecrown.com/images/GTProfile.jpg
On the surface this "fever chart" (a line graph showing variation or periodicity over time) might seem visually simple. Without knowing much about the chart, you can tell that it records altitude over mileage in a race, with the race checkpoints marked with red dotted vertical lines. However, that first impression is deceptive. For me to be able to completely describe what it presents in words, I would have to start out like this: "The Grand Tour Highland Route began at an altitude of about 224 feet. Within a mile, the route descended to 200 feet. At about 3 miles it dropped to 100 feet, then it went up and down between 100 and 200 feet for about 10 miles before dropping to about 50 feet at mile 18 and continuing roughly at this level until the 20-mile mark." I've only gotten through about 1/9 of the data presented! And I'm not presenting it at nearly the resolution that it's being presented in the chart, which shows many variations in altitude that I left out of my description.
The point is that graphics have varying levels of "information density," in Edward Tufte's terminology, and you can't always judge the informativity of a graphic by how many lines or points it has in it. A simple diagram or photograph can be extremely information-rich while a pie chart like the first I presented can say almost nothing. Here are a few common categories of graphics we use in technical settings with some general rules and guidelines about using and producing them.
Diagrams
A diagram is a graphic that shows how an object or process is composed. It makes clear the relationship of the parts of the subject to the whole. Diagrams are useful for communicating a range of types of information including structure, location of components, and location of damage as well as a range of procedures such as assembly, protocol, or repair. A comparison of a well-made diagram with a poorly-made one will help illustrate the principles we should keep in mind when designing diagrams. Figure 4 compares two diagrams accompanying instructions for inserting a battery in a piece of electronic equipment.
Figure 4: Two diagrams for inserting a battery in an electronic device
If you had to put a battery either in the printer on the left or the camera on the right, which would you have an easier time with? Here are a list of principles about putting together diagrams that we can infer from comparing these images:
1. Without sacrificing orientation and context, diagrams should fill the frame with only the parts of the subject that are of interest. Notice the image on the left shows the entire printer, making the user hunt around for the battery location. The camera diagram, on the other hand, only shows in Figs. 3-5 the relevant part of the camera for the battery insertion task, but it shows enough orienting detail that the user will know which part of the camera to operate on.
2. Perspective can and should assist the user in locating key components. The image on the left is a two-dimensional schematic, and it's very difficult to locate the battery in this diagram.
3. If the diagram is being used to illustrate a procedure, the steps must be clearly indicated with numbers and directions of action. The curved arrows in the image on the right do a good job of letting the user anticipate the movement of the parts involved.
4. Use color only where and when it's necessary. Neither of these diagrams needed color to communicate its purpose effectively. Color is expensive to print and will be lost if black-and-white copies of the document are made. If you are going to use color, be mindful of saturation levels, as these will produce different shades of gray in a grayscale copy. As well, keep in mind the cultural color associations we discussed in Chapter Three. Don't make something blue if it's potentially hot or dangerous. Don't make something bright yellow or red if you're trying to indicate safety or comfort.
Photographs
As we just discussed, photographs can be incredibly information-dense. Even in technical settings, they are invaluable for communicating concepts such as your domain or field area, change over time (two photos), or the extent of an effect or injury. Without straying too much into Photography 101, here are some things to keep in mind when making or using photographs in your documents.
1. The rule of thirds. This rule says that photographs create more interest when they are not centered absolutely on their subjects. The rule of thirds divides the image into thirds both vertically and horizontally. The intersections of the dividing lines are "hotspots" for locating elements you wish to foreground and draw attention to. This is an aesthetic theory rather than a perceptually-based one, but you can see its basis in human perception. If the image does not place the subject in the exact center, the eye must move to it after first focusing on the center. The eye movement creates the illusion of movement in the picture, as if the subject is moving into focus rather than the eye itself shifting to bring the subject into the center of the fovea. The rule of thirds and the hotspots place images close to the center of the photograph, so they will be noticed, but require a shift of focus that may make the viewer's mind more attentive and active. Take a look at Figure 5 for an example.
Figure 5: The rule of thirds
This photgraph intrigues the viewer because the center is left open, but the two "actors" in the photo (in this case, my dog and a plastic puppy statue at our vet's office that is perplexing him) are offset diagonally close to two hotspots. The subject of the photograph, therefore, is their interaction.
2. Color. The same considerations apply as with diagrams. A color photo with low contrast between colors will look terrible if copied in black and white (or viewed by someone who has various color-blindness issues). Try to keep contrast and saturation in mind when you use photographs in documents.
3. Legal issues. Of course, if you are going to use a photograph in your document, you are liable for any infringements on copyright, just as with diagrams and other technical graphics (we'll be discussing these issues in some detail later on in the course). However, if your photograph is of a living, identifiable person, you need to seek permission to reproduce from that person. Even if the person has died, the family may retain legal control over use of his/her likeness. It's best to be safe rather than sorry and seek permission.
Charts, tables, and graphs
These are probably the most familiar technical graphics. They present data visually by creating metaphors. The line metaphor of a line graph encourages the viewer to think of the data as a continuous and changing event correlated to some factor, usually time. Pie charts use a circle or "pie" as a metaphor to help the viewer think about percentages or fractions in everyday terms. A bar graph asks us to judge the relative heights of its bars as we would compare the heights of children or buildings. The first thing to remember with technical graphics such as these is that it's important to select the correct metaphor for the relationship you wish to communicate. Here are some common pairings:
· line graphs: change over time, direct correlations between two factors
· fever charts: variability/cyclicity across a range as compared to time or distance
· scatterplots: distribution of a population, correlations between two or more factors
· bar graphs: comparison among quantities or entities
· box-and-whisker plots see example : standard deviation, distribution/overlap of sample populations
· pie charts: percentages
· histogram see example: distribution within a population
Once you've selected the most applicable visualization for your data, there are a few readability principles to keep in mind. We'll discuss ethical principles in a few weeks.
1. Always place a caption or title on the graphic, and label all axes and categories clearly. Make sure to use a large, readable font.
2. Use multiple visual cues to communicate information. Here is an example of insufficient visual cuing for someone who has colorblindness. The chart on the left was colored with insufficient contrast (Figure 6), so it appears to a person with red/green deficiency like the figure on the right. . It's a good idea to take advantage of a simulation such as vischeck to check your images before you publish. This problem could have been avoided by adding a pattern such as a check to one bar. You can use multiple cues in any graphic format. You can dash lines in a line graph, or identify different populations in a scatterplot by using triangles and circles--and by making them different colors or black and white.
Figure 6: Results of a colorblindness simulation on a chart with insufficient color saturation contrast
File Formats
As many of the graphics you will be creating will be digital, it pays to know your way around graphics file formats. Here are some of the common types matched to suitable applications
file extension / file format name / best uses / why.jpg / "JPEG": Joint Photographic Experts Group / photographs / .jpg makes small files from images whose statistics are highly variable (lots of color changes between pixels, as in photographs). However, it will make "smoother" images look pixelated, and it's "lossy," meaning its algorithms result in loss of some of the image information
.gif / Graphics Interchange Format / diagrams/graphics / .gif makes very smooth contours in diagrams and results in relatively small file sizes. .GIF's are supported by all browsers.
.tiff / Tagged-Image File Format / photos or diagrams/graphics / .tiff's are relatively large files that preserve image data lost in conversion to .gif or .jpg. These are good to submit to editors who need to alter the images for size, color, or scale
.bmp / Bitmap / altered photos/diagrams/graphics viewed electronically / .bmp's are large files with almost no compression. They're ideal for sending to editors or peers that need to make changes and are widely supported by browsers and graphics programs
.png / Portable Network Graphics / altered photos/diagrams/graphics viewed electronically / .png files were designed to be readable and workable in a large number of graphics programs. They have lossless compression for 24-bit color. Unfortunately, they are large, and some browsers do not support them. It's best to export a .png as a .jpg or .gif before placing it in a web page.
Lessons in Graphics for Visual Communicators
1. Less is more. If a simple line drawing will communicate effectively, there's no reason to build a complicated animation.
2. For web graphics, think small for file size.
3. Select your graphic with your audience needs and information density and clarity in mind.
4. Use multiple cues in your graphics for readability.
Exercise
Redesign the cover of one of your favorite novels to better reflect the story. Keep in mind the design and perception principles we've learned and the information about graphics we've just covered. Write a short memo (1/2 page double-spaced) explaining what changes you made and why and submit it with your redesign.
References
Tufte, Edward. The Visual Display of Quantitative Information. Graphics Press, 2001. (and Tufte's other works)
http://www.vischeck.com
Geoff Lawrence's Top Ten Photography Tips
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