# Introduction to Computers

## II. Why Use Graphics?

### The basic reason is:  The power of visualization

• Graphics can show words and numbers and data in ways that are meaningful and quickly understood.
• Over half the neurons of the brain are dedicated to the eyes and interpretation of visual information.
• Graphics are the most effective way of helping the user "to see", i.e., to understand.

### Several software packages provide excellent graphics features

• MS-Word
• MS-Excel
• MS-PowerPoint
• WingZ
• We have already demonstrated in the lab how to make a simple pie chart in MS-Excel

### The author points out that graphics may be classified as

• Analytical Graphics
• Presentation Graphics

## III. Analytical Graphics

### Examples:

• Example 1:  Consider the following problem:

### Analyze and display the world's shale oil energy supply by continent.

Table 4.1

Shale Oil Resources of the World

• Copy or type this into the WingZ spreadsheet workspace

• To compute the total resources, type "Total" in A10, and =SUM(B5...B9) in B10. [In Excel, its (B5:B9)]

• Get the result:

• To plot the resulting distribution, select (A5:B9) and drag graph

• Can view this as a pie graph:

### What if each continent uses 20% of their shale oil per year?

• This is computed by simple equation in C5

= 0.8*B5

and dragging down and across.

• Can plot this dependence:

• Example 3:  Can also do some really neat, scientific stuff (demonstrate):

Figure 2.20 Spreadsheet calculation of damped circular wave.

Figure 2.21 WingZ 3D surface plot of damped radial cosine wave.

## IV. Presentation Graphics

### Presentations graphics are professional quality analytical graphics

• Appear created by professional graphics artist
• May include clip art
• May contain animated labels, flying logos
• May contain sound effects

### Software for Presentations Graphics includes:

• MS-Excel
• MS-PowerPoint
• WingZ

### Edward Tufte, in his book, The Visual Display of Quantitatitative Information, gives six principles for graphical  integrity:

1.  The representation of numbers, as physically measured on the surface of the graphics itself, should be directly proportional to the numerical quantities represented.

2.  Clear, detailed, and thorough labeling should be used to defeat graphical distortion and ambiguity.  Write out explanations of the data on the graphic itself.  Label important events in the data.

3.  Show data variation, not design variation  (i.e., avoid "chart junk")

4.  In time-series displays of money, deflated and standardized units of monetary measurement are nearly always better than nominal unit.

5.  The number of information-carrying (variable) dimensions depicted should not exceed the number of dimensions in the data.

6.  Graphics must not quote data out of context.

### Examples of "Chart Junk" and Graphical Distortion

• Question:  What does this graph show?

• That this one doesn't show just as well?

• In fact, I believe that 3D Pie Charts can even distort data.  Consider the following pie chart:

• Obviously, all five quantities have equal areas.  Now display the same data as a 3D Pie Chart:

• Some people without good spatial visualization abilities might conclude yellow is the largest slice.

### Another source of graphical distortion  -  offset axes.

• Note:  Items 4 and 5 differ only by 2%, not 300% as first indicated.
• Your protection is in carefully labeling axes, including "warning labels"

Updated February 2, 2001