Transcript GIS in the Sciences ERTH 4750 (38031) Efficient and effective result presentation with GIS Xiaogang (Marshall) Ma School of Science Rensselaer Polytechnic Institute Tuesday, Apr 16, 2013

GIS in the Sciences
ERTH 4750 (38031)
Efficient and effective result presentation
with GIS
Xiaogang (Marshall) Ma
School of Science
Rensselaer Polytechnic Institute
Tuesday, Apr 16, 2013
Acknowledgements
• This lecture is partly based on:
– Blok, C., 2006. Data visualization. E-lecture of the
Distance Course Principles of GIS. ITC, Enschede, The
Netherlands
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Contents
1.
2.
3.
4.
GIS and maps
The visualization process
Visualization and strategies
The cartographic ‘toolbox’
– data characteristics
– representation of these characteristics
5. Examples, how to map:
– qualitative data
– quantitative data
– (terrain or statistical) elevation, time
6. Map cosmetics: the finishing touch
7. Map dissemination
3
1 GIS and maps
Data Capture and
Preparation
Storage and
Maintenance
Manipulation
and Analysis
Data
Presentation
• In a GIS environment,
maps can be used to:
– Input for GIS
– Communicate GIS
results
– Support spatial analysis
• Maps are not only final
products (output)!
4
Map Characteristics
• Main characteristics of
maps
– 1. Maps provide
answers (in graphical
form) to questions
related to the three
basic components of
geographic data
“Where did the students of a
department come from?”
• geographic location
(Where?)
• thematic attributes
(What?)
• time (When?)
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• Main characteristics of
maps
– 1. Maps provide
answers (in graphical
form) to questions
related to the three
basic components of
geographic data
“What is the type of land use?”
• geographic location
(Where?)
• thematic attributes
(What?)
• time (When?)
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• Main characteristics of
maps
– 1. Maps provide
answers (in graphical
form) to questions
related to the three
basic components of
geographic data
“When did the longest coast line
occur?”
• geographic location
(Where?)
• thematic attributes
(What?)
• time (When?)
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• Main characteristics of
maps
– 2. Maps offer abstract
representations
(models) of reality,
that are:
• simplified
• classified
• symbolized
Details in the aerial photograph are
omitted from the map. For example,
cars are not symbolized in the map.
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• Main characteristics of
maps
– 2. Maps offer abstract
representations
(models) of reality,
that are:
• simplified
• classified
• symbolized
Features in the photo are classified
using predefined criteria. For example,
roadways are classified as major or
minor roadways.
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• Main characteristics of
maps
– 2. Maps offer abstract
representations
(models) of reality,
that are:
• simplified
• classified
• symbolized
Symbolization is used to highlight
differences in features. Major and minor
roadways are symbolized differently.
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Scale
1:5,000
1:1,000,000
Distance
on map
Distance
in reality
Large
scale
1cm
50m
Small
scale
1cm
10km
• Main characteristics of
maps
– 3. Maps are
representations at
scale
Scale: ratio between distance
on the map and corresponding
distance in reality
Maps that show much detail of a small
area are called large-scale maps.
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Scale
1:5,000
1:1,000,000
Distance
on map
Distance
in reality
Large
scale
1cm
50m
Small
scale
1cm
10km
• Main characteristics of
maps
– 3. Maps are
representations at
scale
Scale: ratio between distance
on the map and corresponding
distance in reality
Maps that show less detail of a large
area are called small-scale maps.
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a little more about scale
• Scale indications
– verbal
• e.g. one-inch-to-the mile
– representative fraction
• e.g. 1 : 100 000
– graphical (scale bar)
• suitable in digital environments!
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• Scale indications
– verbal
• e.g. one-inch-to-the mile
– representative fraction
• e.g. 1 : 100 000
– graphical (scale bar)
• suitable in digital environments!
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• Scale indications
– verbal
• e.g. one-inch-to-the mile
– representative fraction
• e.g. 1 : 100 000
– graphical (scale bar)
• suitable in digital environments!
• Digital graphical scale
– Advantage of scale bar in
digital environment is that its
length changes when
zooming in or out
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Definition of a Map
• Now we can have a
definition for the map
• A map is:
– a representation or
abstraction of geographic
reality; a tool for
representing geographic
information in a way that is
visual, digital or tactile.
– a reduced and simplified
representation of (parts of)
These maps can be perceived visually,
the Earth’s surface on a
on a computer screen or printed map
plane.
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• A map is:
– a representation or
abstraction of geographic
reality; a tool for
representing geographic
information in a way that is
visual, digital or tactile.
– a reduced and simplified
representation of (parts of)
the Earth’s surface on a
plane.
These maps are stored in a database
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• A map is:
– a representation or
abstraction of geographic
reality; a tool for
representing geographic
information in a way that is
visual, digital or tactile.
– a reduced and simplified
representation of (parts of)
the Earth’s surface on a
plane.
A tactile map is a map for blind or
seriously visually impaired users, it can
be perceived by touch instead of visually.
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Types of Maps
• Traditional distinction in
maps
– topographic maps
• accurate representation of the
Earth’s topography
– thematic maps
• one or more particular themes
are emphasized
A topographic map of the New
York state.
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(a)
• Traditional distinction in
maps
– topographic maps
• accurate representation of the
Earth’s topography
– thematic maps
• one or more particular themes
are emphasized
(b)
• Less relevant distinction
in a digital environment
(a) New York County Map
(b) New York Rivers Map
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Map dimensions
• You can distinguish types of
maps based on the number
of dimensions used for the
representation:
– Flat (2D)
– Flat + Height (3D)
– Flat + Height + Time (4D)
2 dimensional (flat) representation of
the ITC building and surroundings.
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• You can distinguish types of
maps based on the number
of dimensions used for the
representation:
– Flat (1D, 2D)
– Flat + Height (3D)
– Flat + Height + Time (4D)
3 dimensional (flat + height)
representation of the ITC building.
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• You can distinguish types of
maps based on the number
of dimensions used for the
representation:
–
–
–
–
Flat (1D, 2D)
Flat + Height (3D)
Flat + Height + Time (4D)
Flat + Height + Time + Scale
(5D?)
4 dimensional (flat + height +time)
representation of the ITC building, at
three moments in time during its
construction.
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2 The visualization process
• Maps are the result of a visualization process
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Cartographic Tools
• Visualization methods
and techniques are
applied using
cartographic ‘tools’:
– functions
• (e.g. algorithms)
– rules
• (e.g. generalization,
cartographic grammar)
– habits or conventions
An algorithm can be used to smooth
lines and improve the appearance of
features.
• (e.g. water is represented in
blue)
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• Visualization methods
and techniques are
applied using
cartographic ‘tools’:
– functions
• (e.g. algorithms)
– rules
• (e.g. generalization,
cartographic grammar)
– habits or conventions
Rules tell us to use proportional
symbols to display absolute quantities.
• (e.g. water is represented in
blue)
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• Visualization methods
and techniques are
applied using
cartographic ‘tools’:
– functions
• (e.g. algorithms)
– rules
• (e.g. generalization,
cartographic grammar)
– habits or conventions
Traditionally water is represented in
blue.
• (e.g. water is represented in
blue)
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3 Visualization and strategies
• ‘Visualization’ has several meanings:
– generic: to make info visible (presentation in graphical
form)
– more specific: to use sophisticated computer
technology and ‘toolboxes’ to make data/info visible for
specific use: visual exploration
this process is often called:
• scientific visualization: meant to stimulate thinking
• keywords: interaction, dynamics
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Geovisualization
• Two main strategies of
visualization: exploration,
presentation
– private visual thinking: involves
an individual playing with the
spatial data to determine its
significance
– public visual communication:
concerns maps aimed at a wide
audience
• If maps are visually explored,
we also talk about
geovisualization
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• Geovisualization is accelerated by:
– the possibility to generate maps at any stage in
geoinformation processing
– hard- and software developments
– new output media
– changing needs / expectations of users
– availability of abundant data, from different sources
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Cartographic visualization process
• The cartographic
communication process,
based on “How do I say what
to whom, and is it effective?”
• Information loss or gain:
Information derived by the
map user is not the same as
the information that the
cartographic communication
process started with.
Information loss refers to that fact that not all info put into the map by
the map maker is (usually) extracted by the user. Gain refers to the fact
that, because of background knowledge or experience, uses might also
understand (gain) information that is not really included in the map.
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4 The cartographic ‘toolbox’
• Analysis of the
characteristics of data
– What is the common
‘denominator’? Used for
the title of the map
(theme, area, year)
– What is the nature of the
data or What are the
measurement scales ?
The common denominator refers to a common label for all the
attributes/attribute values that are mapped (here: geological units).
The nature of this data, geologic units, is qualitative and is
measured on a nominal scale.
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Measurement scales are linked to the way in which
people perceive visual variables
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• Basic elements of a map:
–
–
–
–
point symbols
line symbols
area symbols
text
• These elements can all
be varied in appearance
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Bertin’s visual variables
• Bertin’s visual variables:
an elementary way in
which point, line and area
symbols can be graphically
varied.
–
–
–
–
–
–
size
color
value (lightness)
grain/ texture
orientation
form/shape
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• The visual variables enable observers to perceive:
– what belongs together, or is of equal importance
(e.g. all red symbols represent danger)
– order
(e.g. the population density varies from low to high,
represented by light and dark color tints, respectively)
– quantities
(e.g. symbols changing in size with small symbols for
small amounts)
– an instant overview of the whole representation
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5 Examples
• How to map:
–
–
–
–
–
–
qualitative data
absolute quantitative data
relative quantitative data
terrain elevation
thematic data in 3D
time series
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How to map qualitative data
• What is the common
denominator of the data?
Watersheds
• What is the nature of the
data?
qualitative (nominal)
• Solution: Colors of equal
visual weight or brightness
which allow the user to
quickly differentiate between
watersheds.
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How NOT to map qualitative data
Map image suggests differences
in importance, but that is NOT
what you want to communicate
Misuse of bright color results
in attention to specific area on
the map
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How to map absolute quantitative data
• What is the common
denominator of the data?
number of inhabitants
• What is the nature of the
data?
absolute quantitative
• Solution: symbols varying
in size
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How NOT to map absolute quantitative
data
Value does not enable estimation of
differences in absolute quantities,
only order. User is left asking "here
there is more, but how much?"
The applied four-color scheme
makes it impossible to infer whether
red represents more populated areas
than blue. No perception of order.
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How to map relative quantitative data
• What is the common
denominator of the data?
Number of inhabitants/sq km
• What is the nature of the data?
relative quantitative
• Solution: Value has been used
to display the density from low
(light tints) to high (dark tints)
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How NOT to map relative quantitative
data
The values tints are out of sequence,
the user will perceive wrong order
(e.g. darkest is not highest in density)
No perception of order
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How to map the terrain elevation
• Different methods to
map terrain elevation:
–
–
–
–
Contours
Layer tints
Shaded relief
3D view
Cartographic technique where lines
connect points of equal elevation at a
selected interval.
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• Different methods to
map terrain elevation:
–
–
–
–
Contours
Layer tints
Shaded relief
3D view
A cartographic technique of showing relief on
maps by coloring in different shades those
parts which lie between selected levels.
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• Different methods to
map terrain elevation:
–
–
–
–
Contours
Layer tints
Shaded relief
3D view
Cartographic technique where lines
connect points of equal elevation at a
selected interval.
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• Different methods to
map terrain elevation:
–
–
–
–
Contours
Layer tints
Shaded relief
3D view
Cartographic technique where lines
connect points of equal elevation at a
selected interval.
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How to map the thematic data in 3D
• Statistical (socio-economic
data) can also be
represented a an elevated
surface. Here, the
municipalities in the
province of Overijssel are
elevated proportionally to
their number of inhabitants.
The resulting map is called
a 'prism map'
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How to map time series
• Single static map: specific graphic
variables and symbols are used to
indicate change or represent an
event
• Series of Static Maps: A single map
in the series represents a ‘snapshot’
in time. Together, the maps depict a
process of change.
• Animated map: Change is perceived
to happen in a single image by
displaying several snapshots after
each other, just like a video.
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6 Map cosmetics: the finishing touch
1. Additional information
marginal info (or
metadata): makes the
map more usable
2. Adding text improves the
identification of features
3. Contrast improves overall
map legibility
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1. Additional information
marginal info (or
metadata): makes the
map more usable
2. Adding text improves the
identification of features
3. Contrast improves overall
map legibility
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1. Additional information
marginal info (or
metadata): makes the
map more usable
2. Adding text improves the
identification of features
3. Contrast improves overall
map legibility
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6 Map dissemination (output)
• Map design is influenced by:
– data characteristics & user strategies (see before)
– output medium, e.g., paper or screen maps
• Screen maps:
– often smaller
– legend is not always visible
and they enable:
– access to a data base
– links to other data
– embedding in multimedia
– dynamics and interaction
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Web maps
• The Web as output medium increases the functions of
maps:
– insight in spatial data (traditional role)
– interface to additional information / services
– previews of data that can be acquired
• Classification of maps on the Web
– Static maps
– Dynamic maps
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Some historical maps of interest
Leo Belgicus, a map of
the low countries
drawn in the shape of
a lion, by Claes Jansz.
Visscher (II), 1609
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Netherlands Principal Industries,
from Map No. 76863,
by the U.S. Central
Intelligence Agency,
1970
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Monthly Average Temperature,
from The National Atlas of the United States of America, 1970. p.102-103
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Sites for maps of interest
• http://www.lib.utexas.edu/maps/
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Summary
• Role of map in a GIS environment: more than just output
• Basics: how to translate characteristics of spatial data into
symbols on a map, with particular attention to:
– analysis of the measurement scale of the data
– measurement scales can be linked to perception properties of
visual variables
– selection of those variables that best translate the nature of the
data
• After translation of the data, the map has to be finalized to
make it usable (taking care of visual contrast, adding text,
marginal information)
• Finally the map is disseminated to users, e.g. via
hardcopies or the Web
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• Reading assignments for this week
– MapInfo Professional 11.0 User Guide
• Chapter 12 Stylizing your map for presentations and publishing
• Chapter 16 Working with data from a web service
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Next classes
• Friday class:
– Lecture: Dr. Gavin Schmidt, " What are climate models
good for?"
– When: Friday, April 19, 2013 4:00 PM - 5:00 PM
– Where: EMPAC Concert Hall
• Next Tuesday
– Guest lecture: Dr. David Rossiter, Advanced topics in
point pattern analysis
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