Chapter 10: Symbolizing Themes

Summary of principles

Use strong visual variables (saturated colors, thick lines, solid patterns, for example) to emphasize the important parts of a map.  Use weaker visual variables (light, unsaturated colors, thin and dashed lines, sparse patterns) for the background material in a map.  In short, let the map's purpose determine how the map will be displayed.
Whenever possible, create maps that work even when rendered in black and white.
Avoid labeling a map until as late in the map creation process as possible.  Get everything else right first.
Do not use labels in place of symbols.  A map is for displaying the patterns of underlying data.  When you want to present numerical or text data, put it into tables.
In ArcView, separate the function of mapping the data from the function of decorating the map.  The view is for mapping the data.  The layout is for decorating the map.

Exercises 10a and b—using markers and graduated symbols

You can use much more than changes of color to distinguish geographic objects on a map.  Commonly recognized visual variables include

symbol size
shape
orientation 
texture
color hue, value, and saturation
location

Complex symbols, such as those representing polygonal shapes, can be combinations of two or more symbols, such as one symbol for the interior and another for the outline, thereby multiplying the options available for distinguishing symbols.

Using a map to display data means determining how the data will be used to modify the values of the visual variables.  Since in many cases the data are first classified, the nature of the map is specified by associating visual variables with the classifications.

ArcView's Symbol Window provides an interface for modifying these visual variables.  The symbol window is opened from the Window menu, using the ctrl-P keyboard shortcut (question: how could you have determined the shortcut by yourself?), or by double-clicking on a classification symbol within the Legend Editor.

Exercises 10a and 10b ask you to modify the symbolization of themes in a View to create a more effective map.  For these exercises it will be useful to begin with views already created for you.  Here are the steps to follow:

  1. From the ArcView project window, press the Recreate a GTKAV Exercise button, .  (It has exactly the same look as the View's Add theme button, but it does something different here!).  If your project window does not have this button, then install and load  the GTKAV extension before proceeding.
  2. In the Recreate a GTKAV Exercise dialog that opens, navigate to the folder where you installed the GTKAV software (C:/GTKAV/, for instance).  From here navigate to the Data subdirectory.
  3. Chapter 10 is part of Section 1 of the text.  Therefore, select "section1.odb" from the list of options.
  4. ArcView will spend a couple seconds reading this file, and then will ask you to "select an exercise."  Choose exercise 10a (or, in the future, whatever exercise is appropriate).

Laboratory Exercises

Experiment with choices of the visual variables to improve the map you produce while working exercises 10a and 10b.

  1. How can you better distinguish points in the [Towns and Villages] theme from points in the [Airports and Landing Strips] theme?
  2. How can you better distinguish the different classes in the [Roads] theme?
  3. How can you help reduce the visual clutter created by the overlapping features in all the themes?

Here are some additional thought questions:

  1. Why are the themes ordered as they are at the beginning of this exercise?
  2. How, if any, do your answers to questions 1-3 change with the scale of the view?  To experiment, consider using these buttons; make a note of what they do:

   

  1. What does this color do: ?  What is it good for?

Can you develop some principles for visual display of maps?  Here are some things to look for:

  1. What kinds of background colors work best?  Bright ones?  Saturated ones?  Dark ones? Unsaturated ones?
  2. Which provides more contrast among symbols: varying size or color?  What advantages and disadvantages does each approach have for map making?
  3. Experiment with patterns (textures) in the polygonal features.  What kinds of textures interfere least with the map display?
  4. What are some of the problems with relying on color for important distinctions in maps?  Can we make effective maps without using color?

Exercise 10c—creating labels

As you will learn, there are at least four different ways to make a mark on a map in ArcView:

  1. As a symbol for a feature in a theme
  2. As a label or graphic "attached" to the theme
  3. As a label or graphic in a view
  4. As a label or graphic on a layout (see Chapter 22).

You have learned #1.  Exercise 10c shows how to create labels in a view using ArcView's Auto-label tool (#2) and using the Text tool (#3).

Things to watch out for

Creating and, especially, positioning labels on a map can be time consuming for any software.  One trick in ArcView is to position the view so that most features to be labeled are outside the view's extent (the visible area): this greatly speeds up the process.  See Chapter 12 for ways of changing a view's extent.
Labeling is always tricky.  Labels must be positioned, symbolized, and sized to avoid obscuring important map features.  None of this information about position, symbol, or size is contained in the thematic data; if something is not quite right, you might have hours or days of work to redo.  Therefore avoid labeling a map until as late in the map creation process as possible.  Get everything else right first.
Do not use labels in place of proper symbols.  A map displays the patterns of underlying data much better through an appropriate symbolization than by posting the values with labels.  If you have to use labels, you might be better off just making a table of the data.
A View is an image, albeit imperfect, of objects in the "real world."  Therefore avoid drawing things in a View that are really just map artifacts: things like scale bars, legends, miscellaneous texts, north arrows, and so on.  In ArcView, the proper place to put such ancillary "paper world" objects is the Layout (Chapter 22).

Laboratory Exercises

  1. How do you control the appearance of labels?
  2. What are the differences between labels created using the auto-labeler and labels created using the label tool, ?
  3. Can you draw a theme's features on top of any labels?
  4. What do the Graphics|Attach graphics and Graphics|Detach graphics menu items do?
  5. What do these tools do (shown sideways)?  How do the graphics they create differ from features shown in a theme?
  6. Where are the graphics and labels in a view stored after you shut down ArcView?
  7. How can you copy graphics and labels from one view to another?  From one ArcView project to another?

This page was last updated 12 March 2004. It was reformatted.  The "Summary of principles" section was added.  Minor editorial changes were made to clarify portions of the text.