A short introduction to GIS

A Short Introduction to Geographic Information Systems

Xiaogang (Marshall) Ma

School of Science

Rensselaer Polytechnic Institute

Tuesday, January 22, 2013

GIS in the Sciences

ERTH 4750 (38031)

Acknowledgements

• This lecture is partly based on:

– Huisman, O., de By, R.A. (eds.), 2009. Principles of

Geographic Information Systems. ITC Press,

Enschede, The Netherlands

– Fox, P., 2012. Introduction to Geographic Information

Systems for Science. Course lecture at RPI, Troy

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Contents

• 1 The purpose of GIS

• 2 The real world and representations of it

• 3 GIS as a domain of science and technology

• 4 Seven levels of GIS competence

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1 The purpose of GIS

• A few example scenarios

• An urban planner might like

to find out about the urban

fringe growth in her/his city,

and quantify the population

growth that some suburbs

are witnessing. S/he might

also like to understand why

it is these suburbs and not

others.

Urban fringe, Waitara, New Zealand Image courtesy of Quentin Christie

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• A biologist might be

interested to determine

how widespread the

invasive Asian clam in

Lake George was, and to

develop and implement an

eradication plan.


Asian clam identified in Lake George, NY Image courtesy of lakegeorge.com

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• A geological engineer

might want to identify the

best localities for

constructing buildings in an

area with regular

earthquakes by looking at

rock formation

characteristics.


Rock outcrop, North San Francisco Image courtesy of Pascal Calarco

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• A forest manager might

want to optimize timber

production using data on

soil and current tree stand

distributions, in the

presence of a number of

operational constraints,

such as the requirement to

preserve tree diversity.


Timber production Image courtesy of futureforest.eu

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• Various professionals work with data that relates to space,

typically involving positional data.

• Positional data determines where things are, or perhaps

where they were or will be.

Abraham Lincoln Thomas Jefferson George Washington

They worked on ‘positions’ (land survey) before entering politics Images courtesy of wikipedia.org 8


• More precisely, those professionals’ questions are related

to geographic space, which have positional data relative to

the Earth’s surface (georeferenced data).

– There are also positional data of a non-geographic nature.

• A Geographic Information System (GIS) is a computerized

system that helps in maintaining and displaying data about

geographic space.

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1.1 Some fundamental observations

• Our world is constantly changing, and not all changes are

for the better.

– Natural causes: e.g., volcanic eruptions

– Human causes: e.g., land use changes

– Mix / Unclear causes: e.g., El Niño / La Niña events

Grimsvotn volcano, May 21, 2011 Image courtesy of AP / Jon Gustafsson

U.S. Drought of 2012 Image courtesy of The NY Times / Mashid Mohadjerin

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• We, humans, want to understand what is going on in our

world, and to take action(s).

• The fundamental problem in many uses of GIS is that of

understanding phenomena that have (a) a geographic

dimension, and (b) a temporal dimension.

– Spatio-temporal: be of/in space and time

“Everything that happens, happens somewhere in

space and time. ” -- Michael Wegener (University of Dortmund)

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Drought’s Footprint (1930 to present) Image source: National Climatic Data Center, NOAA

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The maps show current and projected forest types. Major changes are

projected for many regions. For example, in the Northeast, under a mid-

range warming scenario, the currently dominant maple-beech-birch

forest type is projected to be completely displaced by other forest types

in a warmer future.

Projected shifts

in forest types

Image source:

http://nca2009.globalchange.gov/

projected-shifts-forest-types

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http://nca2009.globalchange.gov/projected-shifts-forest-types








1.2 Definition of GIS

• We may distinguish three important phases of working with

georeferenced data:

– Data preparation and entry

– Data analysis

– Data presentation

• The three phases may be repeated a number of times

before we are satisfied with the results.

• We can define a GIS as a computerized system that

facilitates the phases of data entry, data analysis and data

presentation especially in cases when we are dealing with

georeferenced data.

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1.3 Spatial data and geoinformation

• Data are representations that can be operated upon by a

computer.

• Metadata are data about data.

• Spatial data are data that contain positional values.

• Geospatial data are spatial data that are georeferenced.

– In the context of GIS, spatial data and geospatial data are regarded

as synonyms of georeferenced data.

• Information is the meaning of data as interpreted by

human beings.

• Geoinformation is information that involves interpretation of

spatial data.

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Image courtesy of Peter Fox

Data Information Knowledge

Context

Presentation

Organization

Integration

Conversation

Creation

Gathering

Experience

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• In GIS, a wider view of QUALITY is important for several

reasons:

– Even source data have been subject to strict quality control, errors

are introduced when these data are input to a GIS.

– A GIS database normally contains data from different sources of

varying quality.

– Most GIS analysis operations will themselves introduce errors.

– Uncertainty in decision-making depends upon quality of base data

and derived information.

– … …

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Comparison of

seven available

digital databases

of the streets in

part of Goleta,

CA, USA

(Goodchild 2011)

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2 The real world

and representations of it

• When dealing with data and information we are usually

trying to represent some part of the real world as it is, as it

was, or perhaps as we think it will be.

– We say ‘some part’ because the real world cannot be represented

completely.

• We use a computer representation of some part of the real

world to enter and store data, analyze the data and

transfer results to humans or to other systems.

Image courtesy of NOAA 19

2.1 Modeling

• A representation of some part of the real world can be

considered a model of that part.

– This allows us to study the model instead of the real world.

• Models come in many different flavors.

– Maps

– Databases

– … …

• Most maps and databases can be considered static

models.

• Dynamic models or process models address changes that

have taken place, are taking place and may take place.

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2.1 Modeling

Dynamic model: break-up of

Pangaea and formation of

modern continents

Static model: map of Pangaea

with present continents outlined

Image courtesy of Wikipedia

Image courtesy of USGS

Pangaea: a supercontinent that

existed about 300 million years ago

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2.2 Maps

• The best known models of the real world are maps.

• A map is always a graphic representation at a certain level

of detail.

– The smaller the scale, the less detail a map can show.

• Cartography: science and art of map making

Map scale increasing

Images made with Google Maps

Image © Bil Keane.

Courtesy of familycircus.com

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2.2 Maps

More examples of maps

Images courtesy of rpi.edu

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2.3 Databases

• A database is a repository for storing large amounts of

data.

– It allows concurrent use.

– It supports storage optimization.

– It supports data integrity.

– It has a query facility.

– It offers query optimization.

• Modern database systems organize the stored data in

tabular format.

Image courtesy of

MapInfo User Guide 24

2.3 Databases

• A database may have many tables, and each table may

have many columns (attributes) and rows (records).

• During database design, it is determined which tables will

be present and which columns each table will have.

• The result of a completed database design is known as the

database schema.

• To define the database schema, we use a language,

commonly known as a data model.

• The definition of a model is called data modeling.

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2.4 Spatial databases

• Spatial databases are a specific type of database.

– Besides traditional administrative data, they can store

representations of real world geographic phenomena for use in a

GIS.

– A spatial database, also called a geodatabase, focuses on

concurrency, storage, integrity, and querying of spatial data.

– A GIS focuses on operating on spatial data with a ‘deep

understanding’ of geographic space.

• A spatial database is used under the assumption that the

relevant spatial phenomena occur in a two- or three-

dimensional Euclidean space.

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2.4 Spatial databases

• Geographic phenomena have

various relationships with each other

and possess spatial, temporal, and

thematic attributes.

• For data management purposes,

phenomena are classified into

thematic data layers.

• Spatial analysis is the generic term

for all manipulations of spatial data

carried out to improve one’s

understanding of the geographic

phenomena that the data represent.

Image courtesy of Jonathan Campbell and Michael Shin 27

3 GIS as a domain of science and

technology

(DiBiase et al. 2006)

Philosophy

Computer

Science

Mathematics

Statistics

Psychology

Landscape

Architecture

Engineering

Various

Application

Domains

Geography

Information

Science &

Technology

Geographic Information Science & Technology

Geographic

Information

Science

Application of

GI Science &

Technology

Geospatial

Technology

From GI System to

GI Science & Technology 28

3.1 Geographic Information Science

• Hmm, a broad S – From GISystems to GIScience

– GIScience: the science behind GISystems technology

• considers fundamental questions raised by the use of systems

and technologies

• is the science needed to keep technology at the cutting edge

Courtesy: http://www.ncgia.ucsb.edu/giscc/units/u002/u002.html

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3.2 Geospatial technology

• Geospatial technology / Geomatics

– Land surveying

– Remote sensing

– Cartography

– Geographic information systems (GIS)

– Global navigation satellite systems (GPS, GLONASS,

Galileo, Compass)

– Photogrammetry

– Geography

– …

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• Global Positioning System (GPS)

– a system of Earth-orbiting satellites transmitting

precisely timed signals

• a similar system deployed by the Russian Federation is called

GLONASS (global navigation satellite system)

• and other systems by EU, China, India, etc.

– signals are received by a special electronic device

• the smallest versions are hand-held and even smaller

– provides direct measurement of position on the Earth's

surface

– location is expressed in latitude/longitude or other

standard system


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• GPS


Image source: AP

Image source: Wikipedia

Image from WWW Image source: Wikipedia 32

• Remote Sensing (RS)

– use of Earth orbiting satellites to capture information

about the surface and atmosphere below

– satellites vary depending on how much detail can be

seen, what parts of the electromagnetic spectrum are

sensed

– signals transmitted to Earth receiving stations where

they are transformed for dissemination as digital images

Courtesy: http://www.ncgia.ucsb.edu/giscc/units/u002/u002.html


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• Two main types of RS

– Passive RS: detect natural radiation (e.g., sunlight) that

is emitted or reflected by the object or surrounding

areas

– Active RS: emits energy (e.g., laser light) in order to

scan objects and areas whereupon a sensor then

detects and measures the radiation that is reflected or

backscattered from the target

Images from:

http://www.rsgisrs.com/rs_types.htm 34

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Night lights of Australia as observed by the Visible Infrared Imaging Radiometer

Suite (VIIRS) on the Suomi NPP satellite in April and October 2012

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More information: http://earthobservatory.nasa.gov/IOTD/view.php?id=80030&src=fb

Fires

• GISystems

– a computerized system that facilitates the entry,

analysis, and presentation of georeferenced data

• GPS and RS are primary data sources for GIS


http://shuttles.rpi.edu/

http://www.flightradar24.com/

Try these:

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4 Seven levels of GIS competence

• Levels of GIS competence in ascending order:

1. Public awareness of GIS and its uses;

2. Basic spatial and computer understanding;

3. Routine use of basic GIS software;

4. Higher-level modeling applications of GIS;

5. Design and development of GIS applications;

6. Design of geographic information systems; and

7. GIS research and development.

(DiBiase et al. 2006; Marble 1997)

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A short introduction to GIS

Technology

Transcript of A short introduction to GIS