Lab 4: Displaying Themes
Table of Contents
1.
Lesson goals
2.
Theme display properties
a) Changing default symbols
b) Symbol palettes
c) Additional symbol palettes
d) Creating a default legend
3.
Communicate a message with your data
a) Thematic mapping
b) Classifying your data
c) Classification types
4.
Exercises
a) Display features based on their attributes
b) Classify features
c) Symbolize themes
5.
View display properties
a) Changing a view's background color
b) Changing the style of the Table of Contents
6.
Adding text to your map
a) Labeling data based on an attribute
b) Customizing labels
c) The Label tools
d) The Text tools
7.
Exercise
a) Label data
8.
Lesson summary
1.
Goals
ArcView GIS gives you
many ways to present your data. In this lesson, you will learn how to:
- set theme display
properties
- display features based on
attributes
- change theme symbology
- create thematic maps and
custom legends
- classify data
- set view display
properties
- customize the default
settings for text labels
2.
Theme display
properties
In
ArcView, you can symbolize theme features in a number of ways. Varying the color,
shape, and fill patterns of different feature types can help your audience
interpret your maps. When creating theme symbology, you should always
choose colors, shapes, and patterns that enhance the map reader's ability
to distinguish between different areas on the map display. A clear legend
facilitates map interpretation. A map that is not understandable is one
that is of no use.
In this map,
each theme has a distinct color and shape. While the symbology may be
basic, this map is easy to understand and therefore useful.
a) Changing
default symbols
To change the colors
and shapes that represent a theme's features (its symbology), you use the
Legend Editor. You open the Legend Editor by double-clicking on the theme
name or symbol in the view's Table of Contents.
Inside
the Legend Editor, you can choose new symbology and preview changes before
applying them to the entire theme. Here, the Legend Editor was used to
change the symbology of the Public water taps. The symbols were changed
from blue circles to green squares.
Here, the Legend Editor was used to
change the symbology of the Public water taps. The symbols were changed
from blue circles to green squares.
b)
Symbol
palettes
To edit theme symbols,
you access the Symbol Window by double-clicking the theme's symbol
in the Legend Editor. The Symbol Window contains five palettes and the
Palette Manager, which you use to save and load custom legend files.
The palettes allow you
to choose from a variety of polygon fill patterns, line patterns, point
symbols, text fonts, and colors to represent theme features.
By using one of five different
palettes (collectively called the Symbol Window), you can change the
symbols used to display a theme.
c)
Additional
symbol palettes
ArcView comes with many
additional symbol and color palettes that you can load using the Palette
Manager. There are custom symbols for the transportation, geology, and
weather industries, for example. ArcView's default symbol palette is named
default.avp.
To load a new palette,
click the Load button in the Palette Manager, move to the symbols
installation directory, then find and select the desired palette file.
Palette files are located in the \arcview\symbols subdirectory. You can
also create custom palettes and import them.
You can load other symbol and color palettes in the
Palette Manager. ArcView's default symbol palette is named default.avp.
d)
Creating a
default legend
If you add a theme from
one of the datasets that comes with ArcView GIS to a view, you'll notice
that the theme displays with a predefined legend, rather than defaulting to
a single symbol. All sample data that comes with ArcView GIS has a
predefined legend applied automatically when you load it.
If you have a
legend file (.avl) in the same folder as the shapefile it applies to,
ArcView GIS Version 3.2 automatically loads and applies the legend when you
load the theme. ArcView knows the legend file is related because it has the
same name as the associated shapefile. Here you see a legend file called
"country.avl" in the same folder as the shapefile "country.shp."
When you add a theme to
a view, ArcView searches the data's folder for a legend file with the same
name as the shapefile. Any legend (.avl) file with the same name in the
same directory as a given shapefile is applied automatically. For example,
if you have a shapefile called Country.shp in the same folder as a legend
file called Country.avl, when you load Country.shp, ArcView loads and
applies Country.avl. Of course, you can still modify the legend in the
Legend Editor after loading the data, if you like.
The shapefile Country.shp has an associated legend
file named Country.avl. When the shapefile is loaded into a view, ArcView
automatically applies the legend, rather than defaulting to a single
symbol.
3.
Communicate a
message with your data
A theme's display is
meant to communicate a message. When defining a theme's display properties
you must consider two issues: the message you are trying to communicate and
who your audience is. Also, bear in mind the audience's ability to
interpret the information presented.
One way to effectively
communicate your message is to assign every feature in a theme a unique
color or group features by an attribute value.
In this map of
Ouakam, every feature is assigned a unique color based on population.
a)
Thematic
mapping
ArcView offers many
methods for displaying your thematic data. For example, you can display your
data graphically using dot density maps, column charts, or proportional pie
charts directly on theme features. The graphics below show these
techniques.
In the top view, the
number of dots per county reflects the density of the population for that
county. A column chart displayed on the theme allows you to compare values
for different attributes associated with each feature. A pie chart can help
you see how attributes compare to each other as well as to the total of all
related values. The bottom view shows the ratio of each group to the total
population. Each circle is sized according to the total population for the
county.
Methods for displaying thematic
data include dot density maps, proportional pie charts, and column charts
directly on theme features.
b)
Classifying
your data
You can group features
into classes using the Legend Editor. The default classification groups
data into five categories based on the Natural Breaks, or Jenks, method of
classification. However, you can easily change the classification.
In the example below,
the Counties theme has been grouped into five categories based on the
Pop_93 field in its theme table.
You can display classes
with a color ramp (in which colors change gradually from the first to the
last symbol). The color ramp used below starts with light red for the class
representing the lowest population and ends with dark red for the class
representing the highest population.
The Population theme has been
grouped into five categories based on the Population field in its theme
table.
c)
Classification
types
When you classify
feature data, the classification method and the number of classes you
specify greatly affects how a theme is displayed and interpreted. Before
classifying, you should carefully consider your data to ensure that the
classification method you choose is appropriate.
In the examples below,
notice how the theme's display changes when the Pop_cntry field values are
grouped into five classes using different classification methods. The
features have been grouped with the Natural
Breaks, Equal
Area (the area they occupy), Standard
Deviation, Equal
Interval (the interval between classes), and the Quantile
(quantity of features in each class) classification methods.
This theme displays a group of
districts which have been classified by their population. The darkest color
on the display represents districts with the highest population. While the
data behind each display is the same, the message presented changes
according to which classification method is applied.
4.
Exercises
a)
Display
features based on their attributes
Step
1 Start ArcView and open the project
If necessary, start
ArcView. From the File menu, choose Open Project and open L03_ex01.apr.
When the project opens,
you see a view with one theme, Districts.
Notice that, by default,
ArcView assigns the same color to all the districts. You'll use the Legend
Editor to display the counties based on population.
Step
2 Open the Legend Editor
Double-click the
Districts theme in the Table of Contents to display the Legend Editor.
The Theme dropdown list
displays the name of the current theme, Districts. The Legend Type field
shows that every feature in the theme is displayed with a single symbol. The
Symbol column displays that symbol.
Step
3 Select a legend type
Click on the Legend
Type down arrow and select Unique Value.
Notice that the look of
the Legend Editor has changed; it displays new choices that apply only to
the Unique Value legend. Each feature with a unique attribute value will be
represented by a unique symbol in the Symbol column. There are no symbols
shown because you haven't yet selected an attribute to symbolize.
Step
4 Select a values field
Click on the Values field
and scroll down in the list until you see Population, then click on it.
Now each county has a
unique symbol in the Symbol column. The Value column lists the Population
value for each district. The Count column tells you how many districts each
symbol represents.
Step
5 Apply changes made in the Legend Editor
Click Apply. If
necessary, minimize the Legend Editor or move it out of the way so you can
see the view.
Each county now has its
own symbol because each has a unique population value. Looking at this map,
you decide that grouping the counties into classes would be better for your
presentation.
Step
6 Change the legend type
If necessary, restore
the Legend Editor. This time, choose Graduated Color from the Legend Type
dropdown list.
The Legend Editor shows
no symbols in the symbol column yet; the Graduated Color legend requires
that you choose an attribute to classify. It divides the counties into
groups based on their attributes. It then assigns colors in graduated
shades to the symbols for the classes.
Step
7 Select a classification field
Click the
Classification Field down arrow. Scroll down and click Population to select
it.
Once you select an
attribute, ArcView applies a default classification method, called Natural
Breaks, to divide the counties into five classes. (You'll learn how to
change the classification method and number of classes later in the
exercise.)
Step
8 Use a different color scheme
Select Green
monochromatic from the Color Ramps dropdown list.
The symbols for the five
classes graduate in color from light green (for counties with the lowest
population) to dark green (for counties with the highest population). This
is called a color ramp.
Step
9 Apply your changes
Click the Apply button.
The view now has a
different symbol for each of the five population classes. The color ramp
makes it easy to see the population distribution.
Step
10 Work with the Dot legend type
Now you'll look at some
of the other legend types to see how they display the population data.
In the Legend Editor,
select Dot from the Legend Type dropdown list.
The Legend Editor shows
a Density Field, where you choose the attribute for density calculations.
It also has a Dot Legend field, used to specify how many people will be
represented by each dot.
Step
11 Select a Density Field
From the Density Field
dropdown list, select Population. Click the Calculate button.
ArcView calculates the
number of people each dot will represent and puts this value in the Dot
Legend field. ArcView takes the size of the window and the screen
resolution into account, so the value it calculates may vary based on your
system's configuration.
Step
12 Apply your changes
Click Apply. ArcView
creates a dot density map in the view.
The dot density map
shows that the population is denser toward the center of the map.
Step
13 Use the Chart legend type
Suppose you want to
target a health campaign to people 60+ years old. The attribute table for the
Districts theme contains an attribute for 0 to 19 year olds, 20 to 59 year
olds, and 60+ year olds.
In the Legend Editor,
select Chart from the Legend Type dropdown list.
A chart legend is the
only legend type that allows you to display multiple attributes of
features. It does this by displaying a chart of selected attribute values
inside each feature.
Step
14 Select the data you want to chart
In the Fields column
(on the left), scroll down and select 0-19_years. Click the Add button to
display this field on the right. Select the 20-59_years field and click Add
to display this field on the right. Finally, select the 60+_years field and
click Add.
The attributes you added
on the right are the attributes ArcView will chart.
Step
15 Select the type of chart you need
In the lower left
corner of the Legend Editor are two chart type buttons, one for a bar chart
and one for a pie chart.
Click on the Bar Chart
button.
ArcView will create a
bar chart inside each feature.
Step
16 Apply your changes
Click Apply, then close
the Legend Editor.
The new map in the view
shows the values of three attributes as a chart inside each feature.
If you want to go on to
the next exercise, leave ArcView open. Otherwise, choose Exit from the File
menu to close ArcView.
a)
Classify
features
In the previous
exercise, you worked with the Legend Editor to change legend types, but
often you may also want to change the number of classes or the way the
classes are divided. Changing classes can affect the way data appears and
how it is interpreted, so it's important to choose a classification method
carefully.
In this exercise, you
will divide a group of counties into high, medium, and low population
classes. You'll create three classes using different classification methods
to see how the map representing county population changes.
Step
1 Start ArcView and open the project
If necessary, start
ArcView. Open L03_ex02.apr.
You see a view of the
Districts theme with no classification applied.
Step
2 Open the Legend Editor
In the view Table of
Contents, double-click the Counties theme to open the Legend Editor. Choose
Graduated Color from the Legend Type dropdown list. Choose Population from
the Classification Field dropdown list.
By default, ArcView
creates five classes using the Natural Breaks method. You want only three
classes, however, and a different classification method.
Step
3 Change the classification type
Click the Classify
button.
The Classification
dialog displays.
Choose Quantile from the
Type dropdown list and 3 from the Number of classes dropdown list.
Click OK.
The Classification
dialog disappears and you're returned to the Legend Editor.
Step
4 Apply your changes
In the Legend Editor,
click Apply.
You can see that the 35
Districts have been divided into three classes. The population range of the
three classes varies widely, however.
The Quantile
classification method divides the number of features into classes, but you
might want to divide the population range into classes instead. To do this,
you'll use the Equal Interval method.
Step
5 Select a different classification type
Click the Classify
button in the Legend Editor. In the Classification dialog, choose Equal
Interval in the Type dropdown list.
Click OK.
Step
6 Apply your changes
Click the Apply button
in the Legend Editor, then close the Legend Editor.
This time, ArcView
divided the entire population range of the counties (from 15,550 to
663,995) into three classes that each have an equal range (216,148). The
number of counties in each class varies, but the intervals between high and
low values in the classes are the same.
Step
7 Close the project
Close the project without
saving. From the File menu, choose Close All. Again from the File menu,
choose Close Project. Click No when you're prompted to save your changes.
You've now seen how to
change classification methods to display your data in different ways.
If you want to go on to
the next exercise, leave ArcView running. Otherwise, choose Exit from the
File menu to close ArcView.
b)
Symbolize
themes
You've seen how
classifying features can change the way a map displays. Now you'll learn
how to change the symbols that represent features. The Legend Editor and
Symbol Window allow you to change the color, size, pattern, and other
properties of map symbols.
In other exercises,
you've classified the counties in the ad campaign map based on population.
You now want to change the colors and symbols used in the map.
Step
1 Start ArcView and open a project
If necessary, start
ArcView.
Open L03_ex03.apr.
When the project opens,
you see a view with four themes: a point, a polygon, and two line themes.
The Districts theme is already classified using the Equal Interval method
and a blue-green monochrome color ramp according to population. The Roads
theme is a line theme in which each road has been classified as either a
major or a minor road.
You want to make the map
more informative and attractive by changing the symbols and colors used to
display the features in each theme.
Step
2 Open the Marker Palette
You can change the
color, size, and symbol for any feature in a theme by editing the symbol in
the Legend Editor and Symbol Window.
In the view Table of
Contents, double-click the “Public water tap” theme to display
the Legend Editor. Double-click the point symbol to open the Marker Palette
in the Symbol Window.
Step
3 Select a marker symbol
Notice that some of the
point symbols in the Marker Palette are solid black and some are green with
a black outline. If you select a solid black marker, the entire symbol will
be one color (whichever color is currently being used by the symbol in the
Legend Editor). If you select a green marker, the symbol will be colored in
the center with a black outline.
Click on any green
point symbol in the Marker Palette. From the Size dropdown box, select 10.
Notice that the symbol
in the Legend Editor has changed.
Step
4 Apply your changes
Click Apply in the
Legend Editor.
The changes you made are
applied to the points in the Cities theme.
Step
5 Select a line symbol
The Roads theme uses two
colors of lines to represent minor and major roads. You'll make them more
distinctive by using a double line symbol for major roads.
In the view Table of
Contents, double-click the Roads theme. The Legend Editor shows the current
symbols.
Double-click the line
symbol next to Major Roads in the Legend Editor. The Pen Palette in the
Symbol Window opens. Click on a double line symbol.
Notice that the symbol
for Major Roads has changed in the Legend Editor.
Step
6 Apply your changes
Click Apply in the
Legend Editor.
The Major Roads symbol
changes in the view.
Step
7 Select an area symbol
You might want to use a
pattern for the Districts theme display. You can choose a different pattern
for each symbol, or you can apply one pattern to all the symbols.
Double-click the
Districts theme in the view. The Legend Editor shows the district symbols.
Double-click the first
symbol in the Legend Editor. The Fill Palette opens.
In the Legend Editor
window, hold down the Shift key and click on the other two symbols to
highlight them as well.
In the Fill Palette,
click on a new fill pattern of your choice.
Notice that all the
symbols in the Legend Editor show the new pattern.
Step
8 Modify the area symbol
You can change the color
of any symbol using the Color Palette. For polygon features, you can change
the color of the fill or the outline. You'll give the district features a
more subtle appearance by changing their outline to gray.
Click on the Color icon
(the one with the paint brush) at the top of the Symbol Window. From the
Color dropdown list, select Outline. Click on a gray-colored square.
Notice that the three
symbols in the Legend Editor now have a gray outline.
Step
9 Apply your changes
Click the Apply button
in the Legend Editor.
The Districts theme
displays the new pattern and outline color.
Step
10 Close the project
From the File menu,
choose Close All. Again from the File menu, choose Close Project. Click No
when you're prompted to save your changes.
You've experimented
with classifying features and changing the symbols used to display them.
This can have great impact on the way the information is interpreted and
how the map is interpreted.
If you're going on with
the exercises, leave ArcView running. Otherwise, choose Exit from the File
menu to close ArcView.
3.
View display
properties
With ArcView GIS, you
control how your views look. You can change the color of the view's background,
or you can keep the default white background. You can also change the font
and symbol styles used in the view's Table of Contents.
a)
Changing a
view's background color
The default view
background color is white. Sometimes, however, you may want to use a
background color that provides more visual interest or conveys meaning.
Changing the view's background color is as easy as setting the view's
properties.
In the View Properties
dialog (accessed by choosing Properties from the View menu) there is a
setting called Background Color. Clicking the Select Color button displays
a Color Picker from which you can choose a color for the background of your
view. When you click OK in the View Properties dialog, the view's
background displays with the color you selected.
Choosing a color in the Color
Picker updates the display field in the View Properties dialog. When you
click OK, the color is applied to the background of your view.
In the view below, the
background color was changed to blue (for water). The background color is
maintained when the view is displayed in a layout.
Applying a
background color can improve the look of your view. Here, blue has been
chosen to represent the ocean.
b)
Changing the
style of the Table of Contents
In ArcView GIS, you can
customize the appearance of the view's Table of Contents (TOC). You can
control line symbol flatness, line and polygon symbol length, and text
attributes (the font and font size and style) displayed. On the View menu
there is a choice called TOC Style. When you select this choice, the Table
of Contents Style Settings dialog displays.
The Table of Contents
is customized using the Table of Contents Style Settings dialog. Here, a
flat line symbol, a short symbol length, and the Tahoma font have been
chosen.
This dialog gives you
control over style elements in your TOC. You can make your line symbols flat
or
give them strong 
or
moderate zigzags 
.
You have four options for the length of line and polygon symbols, from
short 
to
very long 
.
You can change the size,
style, and font of the text, but this changes the text in the TOC only, not
text in the view's map display area. You cannot save custom TOC style
settings to legend files (.avl).
The Tahoma
font, size 10, was specified to produce this TOC. Notice that only the text
in the TOC has been updated to the chosen font and font size. The text in
the view's map display area remains unchanged.
4.
Adding text to
your map
Text labels are a key
component of a theme's display. Labels are useful for giving map readers a
geographic point of reference so that they can identify features in the
theme.
You can interactively
generate text labels for features using the Label tool, or generate them
automatically with the Auto-label function. Furthermore, you can use callout,
bullet leader, banner, and highway shield label styles, to name a few.
After you've added a text label, you can change its color, size, and font
in the Legend Editor.
a)
Labeling data
based on an attribute
You can use values in a
theme attribute table as text labels. To do this, open the Theme Properties
dialog, which you access by choosing Properties from the Theme menu. Inside
the dialog, you specify the field whose values you want to use as text
labels and the label's position on the feature. You can also set the label
to scale with the theme, so that when you zoom in and out on features, the
labels change size also.
Below, a field called
Name is used to label the theme's features with their county names.
The Districts theme uses values
from the Name1 field in its theme attribute table to label each feature.
The text labels are positioned in the center of each feature's area and are
scaled.
You can use the Font
Palette in the Symbol Window to set the size, style, and font of text
labels before you create them, or you can change these properties later. It
is a good idea to choose simple text fonts for text labels. Such fonts
enhance a theme's display and increase map readability. Using hard-to-read
fonts or using too many different fonts for the themes in a view may
distract the map reader.
b)
Customizing
labels
When you're adding text
and labels to several themes in a view, you can save time by editing the
default settings for ArcView's Text and Label tools. By customizing text
and label color and font defaults, you control how they appear when you add
them to a view, and you avoid having to do a lot of subsequent editing. The
Default Settings for Text and Label Tools dialog is accessed by choosing
Text and Label Defaults from the Graphics menu.
The Default
Settings for Text and Label Tools is available from the Graphics menu.
To change the settings
for a particular tool, click on the tool's icon on the left side of the
dialog, then uncheck the Use Symbol Window settings for text check box. The
dialog will change to show the options for the tool you've selected. For
example, the top graphic below shows the default settings for the callout
text tool, and the bottom graphic shows the default settings for the
generic square highway shield.
The default settings for the
callout text tool.
The default settings for the
generic square highway shield.
When you specify default
settings for a particular label or text tool, those settings will be used
when you apply the tool in the view. If you want to change font or other
settings after you've added text to the view, you can double-click on the
label or text to display the Symbol Window, then edit the label's
appearance using the options in the palettes.
c)
The
Label tools
The Label dropdown tools
give you many ways to label theme features. The table below shows each
Label tool, how the label appears in the view, and the name of the label
type.
This table
shows each Label tool, how the label appears in the view, and the name of
the label type.
With callout 
,
bullet leader 
,
and banner tools 
,
you can make attractive labels that are clearly associated with features.
To create callout and bullet leader labels, you must click in the view
where you want the label and drag to the desired label length. To create
the other types of labels, simply click in the view where you want the
label.
This view uses callout labels to
point out cities and "regular" labels for the names of the
country and ocean.
This view uses highway shields to label
freeways, and a banner label for the city name.
This view uses a bullet leader to
label Brunei.
d)
The
Text tools
Like the Label tools,
Text tools are used to add descriptive text to features on a view. While
Label tools use values from a field in the theme attribute table to label
features, with the Text tools, you type the text you want to add into the
Text Properties dialog.
When you click
on the view in the place you want to add text, the Text Properties dialog
appears. Simply type in the label's text, set any of the other properties
you like, and click OK.
There are six Text tools
contained in a dropdown menu on the toolbar. Most of them appear similar to
the Label tools, but there are also Text tools available for drop-shadow
text and spline text. The table below shows the Text tools and examples of
how they look in the view. As with the labels, to create text in the
callout and bullet leader styles, you must click in the view where you want
the text and drag to the desired length.
This table
shows the Text tools and examples of how they look in the view.
5.
Exercise
a)
Label
data
You've seen how classifying
features can change the way your map looks and how you can display map
features based on their attributes. You have also learned how to change the
symbols that represent features.
In this exercise, you
will add text labels to features and customize the view's display
properties.
Step
1 Open the project
If necessary, start
ArcView.
Open the project L03_ex04.apr.
When the project opens,
you see a view with three themes: a point, a line, and a polygon theme. The
Counties.shp theme is already classified using the Equal Interval method
and a blue-green monochrome color ramp. The Interstates & U.S. Hwys
theme is a line theme in which each road has been classified as an
interstate or a highway.
You want to make the map
more informative and attractive by changing and adding text and highway
labels.
Step
2 Change the view's background color
Notice that the view's
background color is white by default. This is usually attractive on the
screen, but the readability of the theme's features could be enhanced by
assigning a new background color.
From the View menu,
choose Properties. In the View Properties dialog, click the Select Color
button.
Click on the light
purple box in the Color Picker, and click OK.
Click OK in the View
Properties dialog to apply the new background color to the view.
Step
3 Label data based on an attribute
You are going to label
the districts with their respective names.
Click on the check box next
to the Public water tap theme name to turn it off. Click on the check box
next to the Roads theme name to turn it off as well.
The view redraws to
reflect your new choices.
Click once on the
Districts theme name in the Table of Contents to make it active. Now it
appears raised in the Table of Contents.
From the Theme menu,
choose Properties. Click the Text Labels icon. Make sure Name1 is the
choice in the Label Field scrolling bar.
Click OK.
From the Theme menu,
choose Auto-label. Check that the
Name1 field is the Label Field and keep all of the other options as the
defaults provided.
Click OK.
Step
4 Customize the label settings
Rather than labeling
every district automatically, now you will manually label some of them
instead.
From the Edit menu,
choose Select All Graphics. Press the Delete key on your keyboard. Before
adding labels, you'll set the default properties for the Label tool. The
labels will be added using the settings you specify.
From the Graphics menu,
choose Text and Label Defaults. The Default settings for text and label
tools dialog appears.
Click on the Label tool
shown in the left side of the dialog.
The rest of the dialog
updates to reflect the available settings for the Label tool.
If it isn't already
blank, remove the checkmark from Use Symbol Window settings for text by
clicking on it.
In the Font scrolling list,
choose Courier New font. Set the size to 12 and the style to Bold Italic.
Click OK.
Click the Label
tool 
.
Click inside the districts you want labeled to add their district names.
If you need to move any
of the labels, use the Pointer tool 
to
select a label and move it to a new location.
Step
5 Using the Highways Label tool
Turn on and make active
the Roads theme.
Zoom in to DRO2 --click
the Zoom In button and drag a box around DRO2.
On the toolbar, click
on the bottom right side of the Label tool 
and hold down the mouse button
to display the dropdown tools. Select the Highway Label tool 
.
From the Theme Menu,
click Properties and change the Label Field to Name2.
In the view, click on
the black Major Road to add the label. The highway name is extracted from
the theme attribute table.
Step
6 Close the project
Close the project
without saving. From the File menu, choose Close All. Again from the File
menu, choose Close Project. Click No when prompted to save your changes.
If you are continuing on
to the lesson quiz or module exam, leave ArcView running. Otherwise, choose
Exit from the File menu to close ArcView.
6.
Summary
Symbols and text make a
map more visually appealing and easier to interpret. Grouping theme features
by data values can add meaning to the map and communicate a message. In
ArcView GIS, it is easy to create custom symbols and classify data.
To change theme
symbology, you work in the Legend Editor, which is accessed by
double-clicking on a theme's name or symbol in the view Table of Contents
(TOC). Double-clicking the theme symbol in the Legend Editor brings up the
Symbol Window, which consists of five palettes: the Marker, Pen, Fill,
Font, and Color palettes. The Symbol Window also contains the Palette Manager,
through which you can save and load custom legends and symbols. (ArcView
comes with many custom symbols for different industries; ESRI's custom
palette files have a .avp extension and are located in the \arcview\symbols
subdirectory on your computer's hard drive.)
When you add a theme to
a view, ArcView searches the data's folder for a legend file with the same
name as the shapefile. Sample data that comes with ArcView GIS has a
predefined legend that is automatically applied when you load one of the
themes. You can still edit the legend in the Legend Editor, if you want,
however.
You can group features
into classes based on some attribute in the theme table. The default
classification method ArcView uses is the Natural Breaks method, but you
can choose to classify data by the Equal Area, Equal Interval, Standard
Deviation, or Quantile methods as well. The method and the number of
classes you specify affects how themes display and how your data is
interpreted. Before choosing a classification method, you should carefully
consider your data to ensure you apply the appropriate method.
You can change how
views display by changing their settings in the View Properties dialog. You
can specify a different background color than the default (white), and you
can modify how symbols and text in the Table of Contents appear. You can
customize the TOC line symbol flatness, font size and style, and line and
polygon symbol length. You cannot, however, save custom TOC style settings
to legend files.
Text labels help map
readers identify theme features. You can generate labels one at a time with
the Label tools or generate them automatically with the Auto-label
function. There are quite a few label styles, including highway shield
label styles, from which you can choose.
To label all features
in a theme automatically with values from a theme table, you open the Theme
Properties dialog and specify the attribute field whose values you want to
use as labels. You can use the Font Palette in the Symbol Window to set the
size, style, and font of text labels before you create the labels. To
actually label the features, simply choose Auto-label from the Theme menu.
You can also change the
default settings for the Text and Label tools so that your custom settings
are applied when those tools are used in the view. If you need to change
font or other settings after you've created labels, double-click the label
to bring up the Text Properties window. Here you can modify label settings.
If you use the Label
dropdown tools, you can specify a field in the theme attribute table whose
values you want as feature labels, and then click in the view on the
features you want labeled. With the Text dropdown tools, on the other hand,
you type your own label text before clicking on a feature.
