Symbology
The guts of
making a decent
map!
1
What’s in the module?
• explore a GIS map and get information about map
features
• preview geographic data and metadata
• add data to a map
• describe the structure of a GIS map
• explain how a GIS represents real-world objects
• change the way features are drawn on a map
• access feature information in different ways
• describe spatial relationships of map features
• describe how GIS can be used to solve problems
2
What is important in the module?
• explore a GIS map and get information about map
features
• preview geographic data and metadata
• add data to a map
• describe the structure of a GIS map
• explain how a GIS represents real-world objects
• change the way features are drawn on a map
• access feature information in different ways
• describe spatial relationships of map features
• describe how GIS can be used to solve problems
3
And imbedded in there is …
• Information on how to decide…
– what you want to communicate to whom.
– On the kind of classification to use to do
that
• That’s why you need to read the stuff
in the text and think about what you
are doing in module 2.
4
An Important Concept
• “Many Factors affect the colors you
choose.
• The perceptual structuring of the
colors should correspond with the
logical structuring in the data…
• Make sure the character and
organization of the colors match the
logic of your data…”1
1
Cynthia Brewer, Designing better maps. ESRI Press
5
And…
• “When choosing map colors, you should not be
overly concerned about which colors your
audience likes. Everyone has an opinion …
Regardless of context , it seems that most
people like blue and do not like yellow… People
like maps with many colors so focus your
attention on presenting your data clearly and
don’t worry about whether you have picked
everyone’s favorite colors.”1
1
Cynthia Brewer, Designing better maps. ESRI Press 6
BUT…
• “When choosing map colors, you should not be
overly concerned about which colors your
audience likes. Everyone has an opinion …
Regardless of context , it seems that most
people like blue and do not like yellow… People
like maps with many colors so focus your
attention on presenting your data clearly and
don’t worry about whether you have picked
everyone’s favorite colors.”1
1
Cynthia Brewer, Designing better maps. ESRI Press 7
And…
• “When choosing map colors, you should not be
overly concerned about which colors your
audience likes. Everyone has an opinion …
Regardless of context , it seems that most
people like blue and do not like yellow… People
like maps with many colors so focus your
attention on presenting your data clearly and
don’t worry about whether you have picked
everyone’s favorite colors.”1
1
Cynthia Brewer, Designing better maps. ESRI Press 8
However
• Usually students don’t have to much
trouble with making decent maps with
reasonable symbolizations
• It comes naturally
• But you do need to keep some things
straight when working with
classifications of data
• And you usually have to classify
9
• Nominal
Data Types
– are categorical data where the order of the
categories is arbitrary
• Ordinal
– categorical data where there is a logical
ordering to the categories
• Interval
– continuous data where differences are
interpretable, but where there is no "natural"
zero
• Ratio
– continuous data where both differences and
ratios are interpretable
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….more
• Quantitative data is numerical
–
–
–
–
–
Ratio, Interval, ordinal data types
continuous data
you are not limited to acuity of the eye
depth-to-bedrock (ratio)
Water table, pollution conc.
• Qualitative data is not necessarily
numeric
– Nominal data – soil type, road classification
– limited to max of 10-12 colors (classes) and you
want contrast – 5 is better yet
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Exercise 2
• Lots of symbols for points, lines, &
polys
• Labeling features –
– Dynamic and Interactive
– Annotation
• Symbolizing based on attribute
– Category
– Quantity
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Quantity
• Graduated colors
– Color ramps – which work best?
• Graduated Symbols (classification)
• Editing legend entries for the TOC
15
Classification
• How many classes
• What method to use for placing the
values into classes
• What kind of symbology to use (e.g.,
graduated colors or graduated
symbols)
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Maps - Categorical
• Categorical symbolization is typically
used for NOMINAL data
– Quite often similar colors will be used
for related categories
– You want the user to be able to discern
the categories
17
Quantitative maps
• Displays quantitative data – interval
or ratio data and even ordinal data
• A graduated ramp or palette is used
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Classifications
• Natural breaks : finds groupings
inherent in the data. Default
• Equal interval : interval between each
class is the same.
• Quantile : each class contains an
equal number of values (features).
• Manual : you decide
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