Symbolization
The key to effective mapping
1
Overview
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•
•
•
Introduction to module 2
Concept of layers
Brewer’s on-line help
Examples
2
Module 2 Lesson 1
• Working with Symbols
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Types of symbols
Choosing symbols
Labeling map features
Display and label map features
Exercis
e
3
Types of Symbols
Lines
Polys
Points
4
Labeling feaures
• Features can be
labeled with data in
the attribute file
• Set up in Layer
Properties
• Turn on and off
with right-click on
layer
5
Module 2 Lesson 2
• Symbolizing features based on
attributes
– Drawing features to show categories
– Drawing features to show quantities
– Display features with categories &
quantities
6
Quantities? Categories?
• Data types:
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–
–
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Nominal
Ordinal
Interval
Ratio
Categorical
Quantities
7
Module 2 Lesson 3
• Classifying data
– Grouping attribute values into classes
– Deciding which classification scheme to
use
– Explore methods of classifying data
– (or – how to lie with maps!)
8
Classify?
• Place data into groups
• 123456 789
•
0
1
2
• By doing this you are saying that:
– The differences between values within a
group are not significant
– Or
– Even if they are I can’t display them
effectively
9
Purpose of Classification
• The most important process involved in
producing a choropleth map
• Values are grouped into classes to simplify and
generalize mapped patterns for the reader.
• Although some details may be lost in
classification, the results allow more
information to be transmitted.
• Minimize the differences within each class and
maximize differences between classes.
• The spatial pattern shown by choropleth map
can be greatly altered by changing the
classification method.
10
Number of classes
• The number of classes determines how
detailed the mapped distribution will be.
• The minimum number of classes is
normally 4.
• The maximum number is eleven (or 12).
• The optimum number is 5 or 6.
• On a monochromatic map (single color
ramp) viewers cannot perceive more than
8 classes
11
The Symbology Tab
• There are actually several ways to
classify the data
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Natural breaks
Equal interval
Quantile
Manual
• This can get quite messy
• AND IT DOES NOT CHANGE THE
DATA!
12
Module 2 Lesson 4
• Mapping density and proportion
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Mapping density using attribute values
Mapping density visually
Mapping proportion
Map density and attribute
relationships
13
So
• There are 4 exercises
• This is harder than Module 1 and you
have to pay attention
• But it is basic theory related to
communicating with maps
14
Overview
•
•
•
•
Introduction to module 2
Concept of layers
Brewer’s on-line help
Examples
15
Layers
• A confusing term since it is used in
several ways
• GIS professionals have used the term
to refer to the layers of data in the
layered structure of gis data….
16
Layers
• A confusing term since it is used in
Skewer of
several ways
location
Streams
• GIS professionals have used the term
to refer to the layers of data in the
Power lines
layered
structure of gis data….
Landuse
Roads
17
Layers
• A confusing term since it is used in
several ways
• GIS professionals have used the term
to refer to the layers of data in the
layered structure of gis data….
• It also has a very specific and
important meaning in ArcGIS
18
Layers in ArcGIS
• When you create a symbology it is
saved in the map document so that
when you reopen the features have he
same symbology
• What if you would like to use the
same symbology in different maps?
• Layer Files to the rescue.
19
Layer Files
•
•
•
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Save the link to the data
And
The symbology used
Then you can add the layer file to any
map using that data
• If it can’t find the data it will not
work!
20
From Help
• In ArcGIS, a reference to a data source,
such as a shapefile, that defines how the
data should be displayed on a map.
• Layers can be stored in map documents
(.mxd) or saved individually as layer files
(.lyr).
• Layers are conceptually similar to themes
in ArcView 3.x that have legend files (.avl)
21
Overview
•
•
•
•
•
Introduction to module 2
Concept of layers
Classification
Brewer’s on-line help
Examples
22
Overview
•
•
•
•
Introduction to module 2
Concept of layers
Brewer’s on-line help
Examples
23
Summary
• ArcGIS, as you will see, contains
hundreds of symbols for points and
lines
• And hundreds of outlines and fills for
polys
• Keeping track of where they are is a
problem
24
Summary
• Classification is the trickiest part of
this module
• And probably the most important
• So read and do the exercises
carefully -- and keep notes
• And, as usual, there are multiple ways
of doing things
25