1 DATA VISUALIZATION
GABRIEL PARODI
STUDY MATERIAL: PRINCIPLES OF GEOGRAPHIC INFORMATION SYSTEMS AN INTRODUCTORY TEXTBOOK CHAPTER 7
Contents
GIS and maps
The visualization process
Visualization and strategies
The cartographic ‘toolbox’
data characteristics,
representation of these characteristics
Examples, how to map:
qualitative data,
quantitative data,
(terrain or statistical) elevation,
time
Map cosmetics: the finishing touch
Map dissemination
GIS and maps
In a GIS environment, maps can be used to:
Input data(scanning/
digitizing existing maps)
Query maps(to find available data, attribute values)
Display resultsof GIS operations Support visual(in stead of
computational)analysis
Maps are not onlyfinalproducts (output)!
Main characteristics of maps
1. Maps provide answers (in graphical form) to questions related to the 3 basic components of geographic data:
geographic location
thematic attributes
time
3
‘Where do the ITC students come from?’
‘What is the type of land use?’
‘When did the longest coastline occur ?’
Where ?
Refers to geographic location (geometry)
What ?
Refers to thematic attributes
When ?
Refers to time
More complex, combined questions are also possible
Maps are efficient and effective means to transfer geo-spatial information to users !
5
Main characteristics of maps
2. Maps offer abstract representations (models) of reality, that are:
simplified
classified
symbolised
Representations of reality
more abstract realistic
Main characteristics of maps
3. Maps are representations at scale
Scale: ratio between distance on the map and corresponding distance in reality
Scale distance distance on map in reality 1 : 5 000 1 cm 50 m
1 : 100 000 1 cm 1 km
large small
Scale indications
verbal
e.g. one-inch-to-the-mile
representative fraction
e.g. 1 : 100 000
graphical (scale bar)
suitable in digital environments!
e.g. 0 50 m
7
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.
There are many types of maps
Topographic map
Thematic maps
watershed areas population density
Tradition distinction in maps
topographic maps
accurate representation of the Earth’s topography
thematic maps
one or more particular themes are emphasized
Less relevant distinction in a digitalenvironment
9
+ height
+ time flat Dimensions in a map
The visualization process
Maps are the result of a visualization process
Visualization methods and techniques are applied using cartographic ‘tools’:
functions
(e.g. algorithms)
rules
(e.g. cartographic grammar, generalisation)
habits or conventions
(e.g. water in represented in blue)
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
11 Two main strategies: exploration, presentation
If mapsare visually explored, we also talk about geovisualization
private
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
Communication:
particularly
relevant for
presentation d information loss or
gain
The cartographic ‘toolbox’
1. 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 ?
13
Measurement scales are linked to the way in which people perceive visual variables
(see further)
Important
The cartographic toolbox
Basic elements of a map:
point symbols
line symbols
area symbols
text
These elements can all be varied in appearance
Basic variations: Bertin’s visual variables
form/ shape
orientation
colour (=hue)
grain/ texture
lightness/ value
size
Important
Bertin’s visual variables
15
The visual variables enable observers to perceive:
what belongs together, or is of equal importance
order
quantities
an instant overview of the whole representation
nominal ordinal interval ratio dimensions of
the plane X X X X
size
(grey) value grain/ texture colour (hue) orientation shape
X X X
X X X
X X X
X
Important
How to map?
1. Qualitative data, e.g. watersheds
colour
Qualitative data: watersheds
value colour + brightness
17 2. Absolute quantitative data,
e.g. number of inhabitants
size
Absolute quantitative data: no. of inhabitants
value colour
3. Relative quantitative data, e.g. population density
value
Relative quantitative data: population density
colour + lightness value (sequence!)
19 4. Elevation: terrain (relief)
shading
layer tints
3D view contours
St. Pietersberg, the Netherlands
5. Elevation: statistical surface, e.g. number of inhabitants
6. Time (change over time)
Single static map
Multiple static maps
Animated map
21 Example of mapping time:
Urban growth of Enschede
Growth of Enschede 800-1998, (view-only animation)
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
23
Contrast improves overall map legibility
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 multi media
dynamics and interaction
The Web as output medium increases the functions of maps:
next to: insight in spatial data (traditional role)
interface to additional information / services
previews of data that can be acquired Classification of maps on the Web
http://kartoweb.itc.nl/webcartography/webmaps/classification.htm http://kartoweb.itc.nl/webcartography/webbook/index1.htm
