Efficient and effective result presentation with GIS

transcript

Xiaogang (Marshall) MaSchool of Science

Rensselaer Polytechnic InstituteTuesday, Apr 16, 2013

GIS in the SciencesERTH 4750 (38031)

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

Contents

1. GIS and maps2. The visualization process3. Visualization and strategies4. 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 touch7. Map dissemination

1 GIS and maps

• 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)!

Data Capture and Preparation

Storage and Maintenance

Manipulation and Analysis

Data Presentation

Map Characteristics

• Main characteristics of maps– 1. Maps provide

answers (in graphical form) to questions related to the three basic components of geographic data• geographic location

(Where?)• thematic attributes

(What?)• time (When?)

“Where did the students of a department come from?”

“What is the type of land use?”

“When did the longest coast line occur?”

• 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.

Features in the photo are classified using predefined criteria. For example, roadways are classified as major or minor roadways.

Symbolization is used to highlight differences in features. Major and minor roadways are symbolized differently.

• 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.

Scale Distance on map

Distance in reality

1:5,000 Large scale

1cm 50m

1:1,000,000 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.

Scale Distance on map

Distance in reality

1:5,000 Large scale

1cm 50m

1:1,000,000 Small scale

1cm 10km

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!

• Digital graphical scale– Advantage of scale bar in

digital environment is that its length changes when zooming in or out

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) the Earth’s surface on a plane.

These maps can be perceived visually, on a computer screen or printed map

These maps are stored in a database

A tactile map is a map for blind or seriously visually impaired users, it can be perceived by touch instead of visually.

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.

• Traditional 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 digital environment

(a) New York County Map(b) New York Rivers Map

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.

• 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.

• 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

4 dimensional (flat + height +time) representation of the ITC building, at three moments in time during its construction.

2 The visualization process

• Maps are the result of a visualization process

Cartographic Tools

• Visualization methods and techniques are applied using cartographic ‘tools’:– functions

• (e.g. algorithms)– rules

• (e.g. generalization, cartographic grammar)

– habits or conventions• (e.g. water is represented in

An algorithm can be used to smooth lines and improve the appearance of features.

Rules tell us to use proportional symbols to display absolute quantities.

Traditionally water is represented in blue.

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

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

• 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

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.

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.

Measurement scales are linked to the way in which people perceive visual variables

• Basic elements of a map:– point symbols– line symbols– area symbols– text

• These elements can all be varied in appearance

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

• 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

5 Examples

• How to map:– qualitative data– absolute quantitative data– relative quantitative data– terrain elevation– thematic data in 3D– time series

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.

How NOT to map qualitative data

Map image suggests differencesin importance, but that is NOTwhat you want to communicate

Misuse of bright color resultsin attention to specific area onthe map

How to map absolute quantitative data

number of inhabitants• What is the nature of the

data?absolute quantitative

• Solution: symbols varying in size

How NOT to map absolute quantitative data

Value does not enable estimation ofdifferences in absolute quantities,only order. User is left asking "herethere is more, but how much?"

The applied four-color schememakes it impossible to infer whetherred represents more populated areasthan blue. No perception of order.

How to map relative quantitative 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)

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

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.

A cartographic technique of showing relief on maps by coloring in different shades those parts which lie between selected levels.

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'

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.

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

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

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

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

Netherlands - Principal Industries, from Map No. 76863, by the U.S. Central Intelligence Agency, 1970

Monthly Average Temperature, from The National Atlas of the United States of America, 1970. p.102-103

Sites for maps of interest

• http://www.lib.utexas.edu/maps/

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

• 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

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

Efficient and effective result presentation with GIS

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