Map Symbolization

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Lab 6: Symbology
https://www.mapbox.com/osm-data-report/
Objective
Learn cartographic considerations and strategies for
representing map features
Overview
❏ Generalization strategies
❏ Data Types
❏ Levels of Measurements
❏ Visual Variables
Maps are created to serve a purpose.
Images:
http://www.sbmtd.gov/maps-and-schedules/system-map.html
http://www.carolmendelmaps.com/mapsb/sb3.html
http://lhcalligraphy.com/maps-santa-barbara-ca
Maps are created to serve a purpose.
When creating a map, it is necessary to generalize
about the world in order to convey specific information.
❏ Cartographic generalization strategies:
– Selection
– Simplification
– Combination
– Locational shift
– Exaggeration
Cartographic generalization strategies:
Selection
Select & represent important features;
omit unimportant ones.
http://www.cartographicperspectives.org/index.php/journal/article/view/cp68-roth-et-al/html
Cartographic generalization strategies:
Simplification
Simplify shapes of features to reduce complexity.
http://www.cartographicperspectives.org/index.php/journal/article/view/cp68-roth-et-al/html
Cartographic generalization strategies:
Combination
Combine features that are close together
into a single feature.
http://www.cartographicperspectives.org/index.php/journal/article/view/cp68-roth-et-al/html
Cartographic generalization strategies:
Locational Shift
Adjust location of a feature to avoid overlap.
http://www.cartographicperspectives.org/index.php/journal/article/view/cp68-roth-et-al/html
Cartographic generalization strategies:
Exaggeration
Exaggerate characteristic aspects of a feature.
http://www.cartographicperspectives.org/index.php/journal/article/view/cp68-roth-et-al/h
tml
❏ Types of Map Data
Qualitative – categorical, descriptive
Quantitative – ordered, numerical
❏ Levels of measurement
– Nominal
Qualitative
– Ordinal
– Interval
Quantitative
– Ratio
Different types of data require different symbolization
strategies
Nominal – categorically
discrete, no orde
• Qualitative data. E.g. State name or Class
name
• Cannot be arranged in some numeric
order
Ordinal – natural order
• Qualitative data used for
measuring rank
• Can be arranged by some
numeric order but there is no
mathematical significance
Temperature: ºF and ºC
• Quantitative data. Used to
measure data which does not
have a true “zero” e.g.
temperature
http://www.wunderground.com/US/Region/US/Temperature.html
http://newavessays.com/news/2009/02/p-38/
• Quantitative data. Used to measure data which
has an absolute zero
Data can be symbolized using
❏ Visual Variables
Shape
Hue
Texture
Size
Graytone value
Orientation
Data can be symbolized using
❏ Visual Variables
Shape
Hue
Texture
Size
Graytone value
Orientation
❏ Visual Variables
❏ Visual Variables
❏ Visual Variables
❏ Visual Variables
❏ Visual Variables
❏ Visual Variables
❏ Visual Variables
…
Reminder!
• All lab materials are on Gauchospace
• Due date: Wednesday November 27th by 11:00 am
Geog W12 Maps and Spatial Reasoning
Lab 6: Map Symbolization
OBJECTIVES
Although seemingly objective representations of the real world, maps are subject to a high degree of
subjectivity in content and presentation. In this exercise you will learn about the generalization inherent in
cartography, as well as the different types of data, types of data, levels of measurement, and visual variables
that are included on maps. We will examine the importance of using symbols appropriate to the data to
understand how cartographic visualizations can be used reveal meaningful spatial trends or perhaps promote
misleading interpretations.
MATERIALS
Internet Browser
BACKGROUND
Key Terms
Generalization
To employ strategic cartographic techniques that reduce the complexities of the
real world for representation on a map. Techniques include selection, simplification,
combination, locational shift, and exaggeration.
Levels of measurement
Categories of measurement according to how they can be treated mathematically.
Measurements can be nominal, ordinal, interval, or ratio.
Qualitative
Involving distinctions based on qualities, kind, or type.
Quantitative
Involving the measurement of quantity or amount.
Normalization
To standardize or make consistent
Introduction
Maps are massive reductions of the reality they represent. If viewed in enough detail, the surface of the Earth
can be infinitely complex. For the sake of clarity, much of reality is suppressed to make maps readable.
Cartographers select relevant information and symbolization schemes to highlight what is important and
exclude what is extraneous. As a result, geometric distortion, scaling, and graphic generalization of data are
often unavoidable elements of cartographic representation.
EXERCISE
Part A. Generalization
One means of generalization that cartographers employ is selection, the retention of more important features
and the omission of the less important ones. Another technique is simplification, reducing complexity so that
the major characteristics of a feature are still identifiable. Combination is a common form of generalization in
which two or more similar features are grouped into one symbol or category. Cartographers may also use
locational shifts which introduce a slight budge to a feature’s location to improve visibility of objects that may
run together. In addition, features may be exaggerated for visibility or to indicate importance.
Spring 2015
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Geog W12 Maps and Spatial Reasoning
A portion of the London underground rail system is shown here to scale, with stations and lines in their
geographic locations.
Below is the same region on the official schematic map distributed by the London Underground. This map
shows relative positions of stations along the rail lines. Transportation system maps typically emphasize
topology, or connective relations, rather than geography.
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Geog W12 Maps and Spatial Reasoning
1. Examine the two maps of the London rail system. Explain in detail what generalization techniques were
employed in creating the schematic diagram. What information was omitted to produce the schematic map?
_____________________________________________________________________________________
_____________________________________________________________________________________
2. Why is a schematic diagram preferred for transportation maps?
_____________________________________________________________________________________
_____________________________________________________________________________________
A geographically accurate, interactive Tube Map can be found on the Tube Journey Planner
(http://tubejp.com/). If you like, spend some time exploring the application to understand the complexities
involved in mapping this extensive transit system.
Part B. Representing Information
Levels of Measurement
Data can be qualitative, portraying a characteristic difference in kind or type, or quantitative, showing an
amount difference in degree. All measurements can be subcategorized according to four levels. The nominal
scale provides qualitative information such as name or class, in which ordering is meaningless. The ordinal
scale, which assigns numbers to objects according to rank order, is quantitative but has no mathematical
significance. For example, ranking states in order of preference indicates relative information, but performing
mathematic operations on rank, such as taking a mean, make little sense. Interval is a category for numerical
measurements that lack a true “zero” value or origin, such as the Celsius temperature scale or mean sea level.
In contrast, ratio is a level of measurement at which numerical information is based on an absolute zero or
origin, such as distance.
Visual Variables
The aim of cartography is to effectively communicate spatial information with a minimum of effort. In fact,
much research has been dedicated to improving the comprehension of symbols, particularly on maps used by
emergency responders. Various symbolization schemes are used to represent information on maps.
Features on maps appear as one of three geometric symbol categories: points, lines, or areas. These symbols
can differ in size (varying in length, width, or area), shape, gray tone value (from light to dark), texture
(varying in pattern), orientation (changing in alignment) or hue (differing in color). There is a logic to the
usage of these six visual variables. Each excels in portraying different qualitative or quantitative variations and
levels of measurement. Typically, to display qualitative information, hue, shape, or texture variables are used.
To display amount or counts, different sizes of symbols are used. To display intensity or density, gray tone is
used. To display movement or direction, orientation is used. A mismatch in data and appropriate symbols may
lead to misjudgments about the map message. As an example, hue and quantitative information usually is not
a good pairing, but there are exceptions. For example, using the traffic light color scheme (green, yellow, red)
to indicate rankings from best to worst, or using the blue to red gradient to represent temperature because
people readily associate these colors to cold and hot.
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Geog W12 Maps and Spatial Reasoning
The following chart depicts the six visual variables and the information they best communicate, according to
convention on map semiotics developed by Jacque Bertin, a French cartographer.
Visual
Variable
Point
Line
Area
Best to show
Size
Quantitative
 Amount
 Counts
Shape
Qualitative
 Name
 Category
Graytone
value
Quantitative
 Intensity
 Density
 Ranking
Hue
Qualitative
 Name
 Category
Texture
Qualitative
 Name
 Category
Orientation
Quantitative
 Movement
 Direction
Based on Monmonier, How to Lie with Maps.
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Geog W12 Maps and Spatial Reasoning
Examples:
Good use of Hue – Qualitative
Political map with country names
population?
Poor use of Hue – Quantitative
Population by country. Which has highest
Graytone would be better for comparisons.
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Geog W12 Maps and Spatial Reasoning
3. For the following maps, list this visual variable combination in use (ex: hue and area, size and point, shape
and point, etc), the levels of measurement represented (nominal, ordinal, interval, or ratio), and discuss if the
symbolization is appropriate. There can be more than one visual variable combo, so list all that apply. (click on
maps to enlarge)
EXAMPLE
EXAMPLE
a. MLB United Countries of Baseball Fan Map
* Visual variable combination(s):
Area and hue
* Level(s) of measurement:
Nominal
* Appropriate?
Yes, hue is appropriate for nominal data because it is
qualitative and does not have an intensity or ranking
order.
Source: http://www.unitedcountriesofbaseball.com. 2007.
b. Life in Los Angeles with modified Chernoff faces.
* Visual variable combination(s):
* Level(s) of measurement:
* Appropriate?
Source: Eugene Turner. 1977.
http://mapdesign.icaci.org/2014/12/mapcarte-353365-life-in-los-angeles-by-eugeneturner-1977/
Spring 2015
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Geog W12 Maps and Spatial Reasoning
c. Napoleon’s March on Moscow.
* Visual variable combination(s):
* Level(s) of measurement:
* Appropriate?
Source: Charles Minard. 1861.
d. Shape of America’s Population Cartogram. NY Times
2000.
* Visual variable combination(s):
* Level(s) of measurement:
* Appropriate?
Source: Andrew Phillips. The New York Times. Dec 2000.
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Geog W12 Maps and Spatial Reasoning
Part C. Classification
Thematic maps show the spatial distribution of one or more specific themes for geographic areas. This portion
of the lab will focus on choropleth maps, a commonly used thematic map in which color or shading of area
features are used to represent categories of attribute values. These maps can indicate spatial patterns of
statistical data and are usually mapped onto political boundaries, such as state or county.
Assuming there are no problems with the original data, some sources of problems with choropleth maps are
the size of areal unit selected (state, county, census tract, etc). The spatial unit makes a difference in the story
a map tells. A pattern that is evident in at a neighborhood scale may be washed out when generalized to a
state level or vice versa.
Presidential Election 2008 results by State and by County
Selection of number of data classes, how they are divided,
and the color scheme also tell a story. Different sets of class
breaks applied to the same data can yield different looking
choropleth maps, as in the figure to the right. Data can be
classed using equal intervals, in which each has the same
width as others (ex: 1-20, 21-40, 41-60). Commonly, this can
result in large differences between the number of cases in
each class, and some classes may not have any cases. With
equal frequency classification (quantiles), each class has the
same, or close to the same, number of cases. This is
equivalent to the idea of percentiles in statistics. Natural
breaks classification is based on the idea that data sometimes
fall into clear groups. Although this can be done “by eye,”
usually statistical methods are used to form natural groups
that minimize variance, means, medians, and outliers.
Alternatively, choropleth maps can be classless or unclassed.
Areas are shaded based on individual values, not divided into
classes, on a continuous scale. Although this makes it harder
to mislead a map user, it results in more complex display
patterns that are difficult to interpret and remember. A
cartographer can also select arbitrary class breaks to
emphasize certain data or introduce bias, a tactic of which map readers should be critical.
Spring 2015
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Geog W12 Maps and Spatial Reasoning
4. Take a look at the map below of United Stated Obesity published by Calorie Lab in 2008.
Source: http://calorielab.com/news/2008/07/02/fattest-states-2008. Last accessed Sept 2009.
Discuss how map symbolization is used to convey a particular message. What are the colors used to signify?
Would you consider this map to be objective? Be sure to evaluate the classification scheme, selection of class
boundaries, and areal units.
_____________________________________________________________________________________
_____________________________________________________________________________________
Part D. On your own
5. Find a recent map online, in a magazine, or newspaper and analyze its symbolization. Discuss the visual
variables, any possible issues you may have with its representation of data, and it’s classification scheme.
Attach a copy of your map to the back of the lab.
_____________________________________________________________________________________
_____________________________________________________________________________________
RELATED LINKS
ColorBrewer by Cindy Brewer, Penn State University.

The Original Color Brewer (http://www.personal.psu.edu/cab38/ColorBrewer/ColorBrewer_intro.html)

Color Brewer 2 (http://colorbrewer2.org/)
Spring 2015
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Geog W12 Maps and Spatial Reasoning
Lab 6: Symbology
Name:
Section:
Part A. Generalization
1. Examine the two maps of the London rail system. Explain in detail what generalization
techniques were employed in creating the schematic diagram. What information was omitted to
produce the schematic map? (1)
2. Why is a schematic diagram preferred for transportation maps? (1)
Part B. Representing Information
3. For the following maps, list this visual variable combination in use (ex: hue and area, size and
point, shape and point, etc), the levels of measurement represented (nominal, ordinal, interval, or
ratio), and discuss if the symbolization is appropriate. There can be more than one visual variable
combo, so list all that apply. (You can download these maps from GauchoSpace and use any image viewer
to view enlargements.) (9)
EXAMPLE
EXAMPLE
a. MLB United Countries of Baseball Fan Map
* Visual variable combination(s):
Area and hue
* Level(s) of measurement:
Nominal
* Appropriate?
Yes, hue is appropriate for nominal data because it
is qualitative and does not have an intensity or
ranking order.
Source: http://www.unitedcountriesofbaseball.com. 2007.
Spring 2015
Page 1 of 4
Geog W12 Maps and Spatial Reasoning
b. Life in Los Angeles with modified Chernoff faces.
* Visual variable combination(s):
* Level(s) of measurement:
* Appropriate?
Source: Eugene Turner. 1977.
http://mapdesign.icaci.org/2014/12/mapcarte-353365-life-in-los-angeles-by-eugeneturner-1977/
c. Napoleon’s March on Moscow.
* Visual variable combination(s):
* Level(s) of measurement:
* Appropriate?
Source: Charles Minard. 1861.
Spring 2015
Page 2 of 4
Geog W12 Maps and Spatial Reasoning
d. Shape of America’s Population Cartogram. NY Times
2000.
* Visual variable combination(s):
* Level(s) of measurement:
* Appropriate?
Source: Andrew Phillips. The New York Times. Dec 2000.
Part C. Classification
4. Take a look at the map below of United Stated Obesity published by Calorie Lab in 2008.
Source: http://calorielab.com/news/2008/07/02/fattest-states-2008. Last accessed Sept 2009.
Discuss how map symbolization is used to convey a particular message. What are the colors used
to signify? Would you consider this map to be objective? Be sure to evaluate the classification
scheme, selection of class boundaries, and areal units. (3)
Spring 2015
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Geog W12 Maps and Spatial Reasoning
Part D. On your own
5. Find a recent map online, in a magazine, or newspaper and analyze its symbolization. Discuss
the visual variables, any possible issues you may have with its representation of data, and it’s
classification scheme. Paste a copy of your map here. (5)
Spring 2015
Page 4 of 4

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