Title: Graphs and Visualization
Course: MSc level academic and professional (information) skills > Section: Part 3. Presentation skills

Learning objectives of graphs and visualization

Learning objectives

After this lesson you will:

- know when to use a graphic/visualization
- know what elements are part of a graphic/visualization
- be able to choose the right graphic/visualization for your data
- be able to make a good graphic/visualization

*be able to do a better job than the examples in this comic:

Preparing good graphics - part 1

What are graphics?

A graphic presentation is anything that is not running (narrative) text. We identify the following types:

- graphs
- illustrations
- maps
- images

General issues for all types of graphics are:
- positioning
- captioning
- referencing
- resolution
- typography
- use of colour

But most important is the question: Why use a graphic? And which graphic is most appropriate in each situation?

Graphics are used when text is not effective in presenting the message. Well-designed graphics effectively communicate information; "One picture is worth a thousand words."
On the other hand, confusing graphics at best irritate the reader and at worst hide or even distort the message. So almost always simpeler is better. If all the required information is present, legible and logical, the reader is informed rather than distracted.

What do you want to say?

When you think about using a graphic instead of text, think about the following:

1. Why use a graphic rather than text?
2. What is the message you want the graph to convey?
3. What kind of graph best conveys your idea?

Tip: When trying to determine what message you want your graph to convey, try writing down the caption and text referring to the proposed graphic. The description you want to give to your graphic should tell you the message that the graphic should contain.

Graphics are floating blocks in a document. The typesetting engine decides where to place them.

For some engines, such as LaTeX, the author can give hints on preferred placement. So, figure or tables are not necessarily directly next to the text. Therefore, the text must refer to the  graphic, in two ways:

- Point it out: Figure 4 shows the distribution of . . .
- Explain it:  Observations were concentrated in the central part . .

Captions

Each graphic must have a caption. A caption should be a brief description of the content of a graphic. Many readers skim the document and only look at the graphics, so the purpose of the graphic should be clear from the caption alone.

Preparing good graphics - part 2

Scalable vs. non-scalable graphics

There are two classes of graphics formats:

1. Scalable formats store mathematical descriptions of their elements; These are often called vector graphics.

2. Non-scalableformats store a grid (matrix) of pixels (“picture elements”). Each pixel has a colour or greyscale value. Pixels are also called rasters, another word for “grid”.

Scalable graphics can be displayed or printed at any resolution; Non-scalable graphics have a fixed resolution.

Example of scalable graphics

The middle figure was prepared at the actual size of the printed figure, therefore it’s the “good” one.
All displayed figures have the exact same information and file size, because they have the same instructions to draw vectors.

Example of non-scalable graphics

Scanning for publication

A common task in thesis production is to scan a printed document, such as a paper map, and reproduce all or part of it as an illustration in the thesis. This requires careful planning to get the correct output resolution. If the resolution is too high, file space is wasted and the document is unwieldy. If the resolution too low, the graphic is illegible and “jagged” (pixelated).

Example of a scan

Preparing good graphics - part 3

Why use color?

There are two reasons to use colour, rather than greyscale, in graphics:

1. Colour is a visual variable and thus can communicate information. It is an alternative or supplement to other visual variables such as size, form, orientation and pattern.

2. Colour is an aesthetic element which can make information more attractive. Caution! “Beauty is in the eye of the beholder”, what is really “attractive”?

Why not use colour?

- Colour can distract, irritate, or even deceive–so don’t use it “just because it’s there”.
- Colour is expensive to print.
- Proper use of colour requires special skills.
- Not everyone can see colour the same way.
- Colour is best avoided unless necessary.

Colour figures printed in greyscale

If a colour figure will also be printed in greyscale, the colours must also be distinguishable when converted only to value and chroma (no hue).

Here is a poor choice of colours, when printed in greyscale.

Colour ramp

Colour gradient of colour progression

For continuous variables you should use a continuous visual variable. For colour, this is the colour ramp. The colour ramp is a sequence of colours. If possible these should be connotative, i.e. imply the meaning of the continuous variable.

Example: A colour ramp created from an “altitude” range, creating gradual tints for the intermediate altitudes.

Example of a connatative colour ramp

Probabilistic assessment of seismic hazard in the United States; Source: Open-File Report 02-420, US Geological Survey (2002)

Contrasting and similar colours

Contrasting colours are those that are clearly separated on the colour circle.

Similar colours to show gradations or sub-classes of similar things

Use of similar colours

For ordinal differences, tints (percentages) of a base colour have to be used, to show that one element is “more” or “less” than another element (darker is more, lighter is less). Examples are population density, temperature, and altitude.

For sub-classes, similar colours are required, but they should not show gradual differences. Often patterns are used for a better distinction.  Examples are the subclasses in soil, geomorphological or geological maps.

Example tint scale:

In this scale, the darkest green should be used for the “densest”, “largest”, “heaviest” etc. The end of the range, and progressively lighter tints should be used for “more dilute”, “smaller”, “lighter” etc.

Typography

Font family

Something that might be forgotten when thinking about the graphics in your paper, but is very important, is the typography. Using the wrong font in your paper can greatly effect its readability.

Here we will start by talking about font families. The typeface (e.g. Roboto) and style (e.g. thin, light, regular, medium, bold, black) form a font family. Adding the size defines a font. The font used in the thesis has a large effect on its readability, and that makes the content more or less accessible.

At the right side of the page you see different examples of the Roboto fonts. Below you see the Qwigley font. Which would you prefer to read?

All about size

Two fonts of the same size will not necessarily appear to be the same size. A font will appear smaller if it has a smaller x-height. Line spacing appears larger if it has an smaller x-height. Look below for an example:

Both fonts have the same font size and line height. Yet the text in the Perpetua font looks smaller, because of its x-height. In contrast the line spacing of the Perpetua font looks larger, making the sentences appear vertically further apart than with the Times New Roman font.

Which font do you prefer? Keep in mind that your preference might not be the preference of your audience. Also the journal you publish in will probably have a preferred or obligatory font for you to use.

Which font is best?

Fonts are optimized for screen (e.g. Georgia) or for printed output (e.g. Times New Roman). So think about the final destination of your paper. Will it probably be printed a lot or will it mostly will be read digital?

Another point of interest is the choice for a sans-serif font or a serif font. Some prefer the first, others the latter. So again it depends on your preference, the medium (on paper or online) etc.
For figures sans-serif typefaces are preferred. Tables on the other hand should use the same font as the running text (a table is not a figure).

Line height, leading

As seen in the section about font size, the line height has an impact on the look of your text. The line height is the amount of vertical space between lines of type. You can adjust the line heigt to be either larger or smaller. Below you see some examples of text in the Times New Roman font with the same font size, but different line height. Next you see an example of two papers using a different line height.

 | Mukagashugi, M.C.(2018) | Acheampong, C.(2018)

Use of type in figures

What do you need to think about when using type in figures? Below you find basic guidlines to help you along.

- Use the same font family and the same base-sizes throughout the whole document.
- Create all illustrations on the correct scale(as used in the document). Re-scaling the illustrations means a change of font size in the final output.
- Use a sans serif font (e.g. Arial, Helvetica, Verdana)
- Use a maximum font size of 11 points and a minimum font size of 7 points, at the output scale.
- Avoid text overlapping/crossing other graphic elements (like lines or patterns) of the same colour.
- Maintain a good contrast between the text and the background.
- Place text in the illustration near the element it is referring to.
- Respect the correct reading direction for the application, e.g. contour values facing uphill.

Use of Tables

Graphical Elements

We discuss each of these in turn:

1. tables

2. graphs

3. illustrations

4. maps

5. images

Use of tables

Large amounts of numerical or descriptive data can generally be better understood than tables. For example this text:

"Of the visitors to the web portal during the trial period, 76% were from Europe (32% The Netherlands, 22% Germany, 9% Belgium, 5% France, 5% United Kingdom, 3% other European) and 24% from the rest of the world (10% Americas, 12% Asia/Pacific, 2% Africa)."

A better option is to present this results as a table and comment on it in the text:

"Visitors to the web portal were predominantly from Europe, especially The Netherlands and Germany (Table X)"

Table X: Web site visitors, location (%)

When not to use a table

Conversely, a few numbers should be presented in the text and do not require a table. For example, the following table:

This information would be much better presented as: “Twenty of the thirty soil profiles showed signs of subsoil wetness.”

Table design guidelines

Here we will give an overview of design guidelines to keep in mind when using tables.

- Tables should be understandable without reference to the text.

The text should comment on and interpret a table, but should not be needed to understand its contents.

- Each table must have a caption, which is understandable without reference to the text. This is repeated in the List of Tables.

- Each column and row must have a heading which very briefly identifies it.

- A table should be as simple as possible, given the information it must present.

- The position of data items in the table should be as intuitive as possible.

- All rows, columns, sub-rows or columns etc. must be clearly labelled so the reader can tell to what a particular item (cell) refers.

- The same data should generally not be presented in the text, table, and figures. Avoid phrases like:

“According to Table X, 35.3% of the respondents preferred the first option . . . ”
But, the table already gives the exact number, so the text does not need to repeat it; instead, the text comments on it:
“A substantial minority of the respondents preferred the first option . . . (Table X).”

Here the author interprets (“substantial minority”) the exact number (35.3%) shown in the table, and relates it to the overall argument.

- Use of symbols, units and terms in tables should agree with the text.

For example, a column heading “water bodies” in the table should not correspond to a category called “lakes” in the text.

- If categories given in rows and columns are naturally ordered, this should be respected in the table.

For example, educational levels “none”, “primary”, “secondary”, “tertiary” should follow this order in rows or columns.

- Tables must be numbered sequentially, either by chapter or for the whole document. They must be referenced in the text, either in parentheses or as a noun (subject or object):

Table 3 shows the model parameters.
The model parameters are shown in Table 3.
Initial model parameters were set according to literature (Table 3).

Use of graphs

Graphs are used to report the results of exploratory data analysis (looking for patterns), or statistical analysis (interpreted results). When you choose to use a graph it must contribute to the argument. You should not use a graph simply to add a picture to your work, it should always be useful and show something text alone can't do.
A graph must be labelled, captioned, and referred to in the text and the graph type match the nature of the variables and their relation. As you can see in the picture to the right, there are a lot of different graph types to choose from.

Next we will show some examples of regularly used graphs.

Scatterplots

Missing information (left); complete information (right).

Classified scatterplots

Showing three species; with legend, by symbol (left) and colour (right).

Use of lines to show interpretation

Note that the lines force an interpretation on the reader.

Histograms

These show univariate distribution; plain (left), enhanced (right).

Time series

The Y-axis is some variable as a function of the X-axis, which is a time sequence.

Use of illustrations

Line drawings are original artwork that illustrate some apparatus (e.g. schematic diagrams) or procedure (e.g. flow diagrams).  They are usually monochrome (either black-white or with some grey-scale shading), but may have colour elements if these add to the reader’s understanding.
They should be legible and as simple as possible, while showing the required information. Furthermore, they must be labelled, captioned, and referred to in the text.

Example flow diagram

Example from Lucidchart

Be aware that symbols have a meaning. Follow the general standards so the symbols are easy to understand for readers and add a legend.

Use of maps

Maps are a special class of figure that present geographical information. Geometrically-correct maps must include enough information to determine theme, location, scale and orientation. Also maps must be georeferenced, at least implicitly. An exception to this are topological maps. You can use tools like Arcmap, ArcGIS and Erdas to add georeferencing to your map.

Colour in a map must not be confusing and, if possible, should be connotative. See the example below. If there is water on a map is makes senses to give this the colour blue. If you use orange instead, people are more likely to think that it is a road for example.

Incorrect use of map colours

Soil types, Edgecombe Country, NC (USA)

In this map highly-contrasting colours are used for similar soils. This can create confusion, because the highly contrasting colours imply (great) differences instead of similarity. The colours you use in a map should make sense. Similar objects on the map should have similar colours. So water in a map should be blue. If you want to show the difference between, for example, seawater and freshwater, don't make the one blue and the other red. Give them both a different shade of blue.

Connotative colours

Connotative colours suggest something about the class from the visual perception. For example:

- blue = water
- dark blue = deep water (ocean)
- light blue = shallow water (ponds, streams)

The choice for certain colours can be established conventions in a given type of mapping. An example from soil mapping is purple for organic soils, blue for clayey soils, browns for loamy soils and yellow for sandy soils.

Standards for Geological maps: Selection of Colors and Patterns for Geologic Maps of the U.S. Geological Survey, http://pubs.usgs.gov/tm/2005/11B01/05tm11b01.html

Example of connotative map colours

Soil map units, Middachten estate, Dieren (NL)

This is an example of a good use of connotative colours in a map. Colour is used to show soil moisture, the controlling factor for land use in this area.

Use of images

Images are bitmapped graphics which should only be used when an actual image is needed, and not as a rasterized drawing. Images that can be presented are screen dumps, photographs, scans of paper maps, and remote sensing imagery.

- Screen dumps (or screenshots) illustrate specific processing steps. They should not be used for program output.

- Photographs should help the reader visualize a complex object that can not be adequately described in words.

Pay careful attention to resolution. You should not only pay attention to the legibility of images, but also to the type and capabilities of the output device. Not every system can for example read or open every image type (e.g. bmp, jpg, png). Also an image with a very high resolution can sometimes also be too large for certain systems to process. So be aware of the end use(r) of your image.

Soil Map of the United States, Section 7. Atlas of American ...
David Rumsey Map Collection

Photographs

Photographs can help the reader to visualize a complex object that can not be adequately described in words. For example a landscape or an apparatus. They can also help the reader appreciate how a procedure was carried out (e.g. a field sampling). A photograph should be used when "a picture is worth a thousand words", so when visualization can explain more than a text description could.

Soil System Sciences | Soil color never lies EGU Blogs -European Geosciences Union
Soil colourdetermination. Credit: Flickr user Soil Science @ NC State.

Effective use of photographs

If you want to make effective use of photgraphs you should show the object of interest as clearly as possible, without distractions. In the example below the object of interest is the first stage of dune stabilization. Do not use a photograph with another subject is as, such as an animal or a person. This only leads to distraction and can possibly even lead to misinterpretation. Also the subject mentioned in the text should be obvious.

“Dune stabilization begins with small patches of grass (Figure X), which stabilization in turns promote more grass in a positive feedback loop.”

Figure X: First stage of dune stabilization; Kootwijkerzand (NL)

Overview and detail photos

Sometimes both an overview and a detail photo should be included side-by-side. For example:

“Weathering can proceed rapidly even in cool climates. Figure X shows a memorial stone engraved in 1921. The detail (right) shows clearly the pitting of the granite, with the resistant quartz grains standing out prominently, and the accumulation of moss on the surface.”

What kind of graphic will best communicate?

In the previous sections we have treated a lot of different types of graphics. Sometimes it is easy to know which one will work best, but sometimes it can be difficult to determine the best choice. So let's get an example and see how we can try to work this problem out.

The example here is from:
TikZ and PGF, Manual for Version 2.00 (2007)
Till Tantau; http://sourceforge.net/projects/pgf

Text:
At the end of a seminar a lecturer asked the participants for feedback. Of the 50 participants, 30 returned the feedback form.
According to the feedback, three participants considered the seminar “very good,” nine considered it “good,” ten “ok,” eight “bad,” and no one thought that the seminar was “very bad.”

As a table

All the information is here and accessible. It is easier to find a specific number in this table than in the text.

As a bar chart

“Looks nice” (?), at least the classes are in correct order, but . . . Can the bar chart answer the following questions?

- How many participants were there?
- How many participants returned the feedback form?
- What percentage of the participants returned the feedback form?
- How many participants checked “very good”?
- What percentage out of all participants checked “very good”?
- Did more than a quarter of the participants check “bad” or “very bad”?
- What percentage of the participants that returned the form checked “very good”?

As you see the bar chart lacks some important information. Let's take a closer look at the graphic faults in this 3D bar chart.

1. The whole graphic is dominated by irritating background lines.
2. It is not clear what the numbers at the left mean. Presumably they are percentages, but they might also be the absolute number of participants.
3. The labels at the bottom are rotated, making them hard to read.
4. The third dimension adds complexity to the graphic without adding information.
5. The three dimensional setup makes it much harder to gauge the height of the bars correctly. For example, consider the "bad' bar. Does the number of this bar stand for more than 20 or less? While the front of the bar is below the 20 line, the back of the bar (which counts) is above.
6. It is imposible to tell which numbers are represented by the bars.
7. What do the bar heights add up to? Is it 100% or 60%?
8. Does the bar for "very bad" represent 0 or 1?
9. Why are the bars blue?

Above we have a whole list of things that don't work with the bar chart. Maybe you have found even more. We can however conclude for sure that the bar chart is not the right choice of graphic for this example. Let's take a look at a graphic that does work.

This seems to be the graphic that says it all. Note the connotative colours, the even treatment of each class, the natural order, the complete information. This graphic shows exactly what you want it to show.
Conclusion; don't just choose a graphic at random. Think about what information it should contain and keep the graphic "clean" and simple. And even more: the message must be clear to the reader.

Recommended steps to come to a good graphic

1. The known issues: Author guidelines.

- Maximum allowed dimensions
- Allowed use of colour
- Formats
- ....

2. The idea: Identify the need for a figure.

- What should it communicate?
- Where should it be placed in the argument?
- How does it complement the text?

3. The content: Specify the minimal required content of the illustration.
4. The sketch: See below; don’t use the computer yet!
5. The realisation: Now do the actual layout, design, and production in the chosen program.

How to sketch

1. Determine the simplest possible illustration for the point you want to make.

2. Make a sketch on paper to more or less the correct scale.
- It’s no problem if your drawing skills are poor, it even helps in forcing to keep things simple.

3. When drawing on paper do not focus on visualization aspects such as colour, fonts, shadows etc.; only consider the content.

4. Do not include elements that are redundant like cell-lines in a table. The human eye and brain is well-suited to discover patterns.

Layout & Design

Here are some tips for effective design.

- Design to scale, effectively using the available space
- Use a consistent design: specify type, colour, lines, symbols and graphic elements and use them consistently.
- Use a consistent and legible typeface for text; best for illustrations is a sans-serif face such as Arial.
- Decide if colour is really required to make your point–would it really enhance the information content? If required, than make a decision on the colour palette to use.
- Variation in line styles (full, dashed, thickness) can create a good visual hierarchy.
- When using symbols in a diagram, graph or map make sure they are visually-distinct and if possible related somehow to what they represent.
- Do not use too many different symbols, they are difficult to distinguish.
- Graphic elements are non-functional, but visual elements to enhance the attractiveness of an illustration. Examples are drop-shadows and shaded backgrounds. If used, use consistently.
- Distinguish figure (the main information) from ground (background, orientating)

Example of figure and ground (routemap)

Let's take a look at an example of the last tip; distinguish figure (the main information) from ground (background, orientating)

So why is the left map bad and the right map good? The left map has more colours and less contrast, which makes it harder to distiguish the route from the other parts in the map. The right map has more contrast and one clear colour that is easily distiguished from the background.

Contrast

Contrast is the difference in colour and light between parts of an image or illustration. It can be used to show the relation between figure and ground and distinguish different elements in a figure.

Balance

Another point of interest is to choose an appropriate balance. Below you see some examples.

Tools for constructing graphics

There are three routes to making graphics:

1. Direct output from an analysis program;
- Statistical analysis: R, SPSS, Systat . . .
- GIS: ArcGIS, ILWIS, GRASS . . .
- “Office” programs: Excel, Word, Open Office, iWork, . . .

2. Drawn in a dedicated graphics program;
- Adobe Illustrator, Visio, Gimp . . .

3. Output from an analysis program and enhanced in a specialized graphics
program.
- Enhancement must not distort or mis-represent!

To summarize...

- Think hard about why you want to use graphics; what type of graphic will best communicate your message.

- Then, design your graphic to be as simple as possible (but no simpler), while still communicating the message.

- Think as hard about your graphics as your text . . . or maybe harder!

      o   More people will look at your graphics than read the text

      o   Graphics make a very strong impression on the reader!

              o  Sloppy, inconsistent, useless, unintelligible? The author might be similar confused and careless about their research.

              o  Neat, consistent, informative? The author is probably a careful scientist.

- It should be clear from this lesson that effective use of graphics is not simple.

- The advantage of good graphic presentation is effective communication of research.

- Poor graphics reflect poorly on the researcher and can be worse than nothing.

- Good graphics, intelligently placed, well-constructed, and contributing to the argument considerably enhance the presentation of research.

- In writing, omit needless words; in graphics, omit needless elements - both of these serve to emphasize the message.

- Do not be satisfied with the default output.

*with thanks to Wim Ferringa (University of Twente) for the content.