gis

Geographic Information Systems and Scienceby Longley, P.A. Goodchild, M.F., Maguire, D.J. and Rhind, D.W.

Concepts & Techniques of Geographic Information Systems by Lo and Albert K.W. Yeung

Text Books

Objectives

• To introduce concepts and the techniques of handling geographical data through a particular form of information system - GIS;

• To introduce the skills and techniques to input, manage, analyse and display spatial information; and

• To introduce the concepts and techniques for spatial data analysis and modelling.

Outline1. What is a GIS?

2. Representing the real world

3. GIS software

4. The nature of geographical data

5. GIS data modelling

6. Geographical databases

7. Geographical query

8. Spatial analysis

9. Digital terrain modelling

10. Network analysis

11. GIS as decision making tool

12. GIS applications

Graphics are Graphics are holistic:holistic:““a picture says more than a thousand words...”a picture says more than a thousand words...”

““First road left, then First road left, then cross the railroad cross the railroad and continue until and continue until you cross the river, you cross the river, then the first right then the first right and right again on and right again on the crossroads...”the crossroads...”

IntroductionIntroduction

Why Use GraphicsWhy Use Graphics

What is a GIS?What is a GIS?A GIS is a database management system for A GIS is a database management system for spatiallyspatially distributed features and the associated attributes.distributed features and the associated attributes.

• Spatial data captureSpatial data capture• ManagementManagement• AnalysisAnalysis• DisplayDisplay• Decision makingDecision making• ResearchResearch

WHAT IS A GIS ?WHAT IS A GIS ?GEOGRAPHICGEOGRAPHIC implies that locations of the data items are known, or implies that locations of the data items are known, or

can be calculated, in terms of Geographic can be calculated, in terms of Geographic coordinatescoordinates ( (LatitudeLatitude, , LongitudeLongitude))

INFORMATIONINFORMATION implies that the data in a GIS are organized to yield implies that the data in a GIS are organized to yield useful knowledge, useful knowledge, e.ge.g

• colored maps and images, colored maps and images, • statistical graphics, statistical graphics, • tables, and tables, and • various on-screen responses to interactive queriesvarious on-screen responses to interactive queries..

SYSTEMSYSTEM implies that a GIS is made up from several inter-related and linked implies that a GIS is made up from several inter-related and linked components with different functions. components with different functions.

Thus, GIS have functional capabilities for data capture, input, Thus, GIS have functional capabilities for data capture, input, manipulation, transformation, visualization, combinations, query, analysis, manipulation, transformation, visualization, combinations, query, analysis, modelling and output.modelling and output.

A container of maps in digital form

A computerised tool for solving geographical problems

A mechanised inventory of geographically distributed features and facilities

A tool for revealing what is otherwise invisible in geographical information

A tool for performing operations on geographical data more efficiently

A spatial decision support system

Definitions of a GIS and the groups who find them useful (from Longley, et al., 2001, pp. 10)

Some DefinitionsSome Definitions

•Government: where to locate public facilities (e.g. schools, hospitals and police stations)?

•Transportation: where to build the new highway that serves most critical bottleneck of the road network?

•Commercial: where to build new shops or good distribution centres that make most cost effective services?

•Travellers: where am I and how can I travel from Jeddah International Airport to Taif University?

•Country park management: where to locate ring roads in Hada that provide the best scenery for driving at different levels with the minimum impact on the environment?

Examples of geographical problems

Components of GISComponents of GIS

A working GIS systemA working GIS system

integrates these five key components:integrates these five key components:

HardwareHardware SoftwareSoftware DataData PeoplePeople

Methods/TraininMethods/Trainingg

HardwareHardware comprises the equipment needed to support the many activities of GIS.e.g. data collection and data analysis.

The central piece of equipment is the workstation, which runs the GIS software

• Data collection requires the use ofDigitizer for conversion of hard copy data to digital data GPS data logger to collect data in the field.

The advent of web-enabled GIS, web servers have also become an important piece of equipment for GIS.

Software

• Software is essential for creating, editing and analyzing spatial and attribute data

• e.g. Xtools, Arc View

Data

• Data is the core of any GIS.

• There are two primary types of data that are used in GIS.

– Geodatabase: is a database that is in some way referenced to locations on the earth.

• Geodatabases are grouped into two different types: vector and raster.

– Attribute data. Attribute data generally defines additional

information, which can then be tied to spatial data.

People

• Well-trained people knowledgeable in spatial analysis and skilled in using GIS software are essential to the GIS process.

• There are three factors to the people component: – education, career path, and networking.

• A person highly skilled in GIS analysis should not seek a job as a GIS developer if they haven’t taken the necessary programming classes.

• Finally, continuous networking with other GIS professionals is essential for the exchange of ideas as well as a support community.

Training

• People working with GIS software must be well trained how to use them.

BASIC FUNCTIONS OF GISBASIC FUNCTIONS OF GIS

WHAT IS IT….?WHAT IS IT….?(LOCATIONS)(LOCATIONS)

Taif AreaTaif Area

(X,Y)

WHERE IS IT ….?WHERE IS IT ….?(CONDITIONS)(CONDITIONS)

WITHIN THE WITHIN THE Subra AreaSubra Area

HOW HAS IT HOW HAS IT CHANGED …?CHANGED …?(TRENDS)(TRENDS)

IMPROVEMENT INIMPROVEMENT INGROWTHGROWTHIN FIVE YEARSIN FIVE YEARS

WHICH DATA AREWHICH DATA ARERELATED ….?RELATED ….?(PATTERNS)(PATTERNS)

NEARESTNEARESTSafaSafa

WHAT IF….?WHAT IF….?(MODELS)(MODELS)

FINDING SOLUTIONS TO FINDING SOLUTIONS TO THE THIRD QUESTIONSTHE THIRD QUESTIONS

BASIC FUNCTIONS OF GISBASIC FUNCTIONS OF GIS

• DATA AQUISITION AND DATA AQUISITION AND PREPROCESSINGPREPROCESSING

DIGITIZINGDIGITIZING EDITINGEDITING

TOPOLOGY BUILDINGTOPOLOGY BUILDING

PROJECTIONPROJECTION ATTRIBUTIONATTRIBUTION

WHY GIS ?WHY GIS ?

• To inventory and monitor resourcesTo inventory and monitor resources

• To test the sensitivity of our analysis To test the sensitivity of our analysis assumptionsassumptions

• To simulate potential impacts of To simulate potential impacts of management alternativesmanagement alternatives

• To make the map the 2nd time, the 50th To make the map the 2nd time, the 50th time, the 100th time...time, the 100th time...

ADVANTAGES OF GIS IN SIMPLE TERMSADVANTAGES OF GIS IN SIMPLE TERMS

• Though collection of data is difficult once it is Though collection of data is difficult once it is collected, it can be stored safely in digital form (in collected, it can be stored safely in digital form (in computer) forever without damage, which usually computer) forever without damage, which usually happens to our maps.happens to our maps.

• Once if a map is prepared accurately it can be printed Once if a map is prepared accurately it can be printed in any scale without any redrawing.in any scale without any redrawing.

• Large scale maps at smaller units (Beats) level can be Large scale maps at smaller units (Beats) level can be joined for creating maps at divisions or district level, joined for creating maps at divisions or district level, very accurately within few minutes.very accurately within few minutes.

Contd..Contd..

Changes can be incorporated very easily Changes can be incorporated very easily in computer and it doesn’t require any in computer and it doesn’t require any redrawing.redrawing.

Same map can be generated even after Same map can be generated even after 100s of years later.100s of years later.

New things can be known after overlay New things can be known after overlay of different themes and a new types of of different themes and a new types of maps can be generated.maps can be generated.

Work can be done faster than manually.Work can be done faster than manually.

The work of decision makers and end The work of decision makers and end users will become easier.users will become easier.

ADVANTAGES OF GIS IN SIMPLE ADVANTAGES OF GIS IN SIMPLE TERMSTERMS

OriginOrigin

The Cave Paintings

1351The Medici sea atlas is published that contains a ‘world’ map.

1375 The Catalan atlas is prepared by Catalan cartographers who made great contribution in the completion of reformation of world map.

1477The first printed edition of the ‘Geography’, Bologna is published on the basis of manuscript atlases, produced by Dominus Nicholaus Germanus

Cave Paintings are considered to be the first GIS Maps as some unknown information (attributes) is linked to it.

A. Cave Paintings have graphic information regarding the animals and their tracks of migration.

B. These paintings used to get shared with in the tribe groups through generations.

C. Most of the ancient civilizations are found by its Cave Paintings.

1.Mesapotomia

2.Central Asia

Manual MappingManual Mapping

Manual MappingDr.John Snow in 1854 used London City Map to Depict

Cholera effected areas.

•Dr.John snow has used a manual Map to track the cholera effected area of the central London, which has been ultimately resulted in finding a contaminated well. This is considered as the first GIS analysis in the world.

•Europeans produced first Manual Maps to travel over seas.(Vascodigama,Columbus).

• In American Rervolution Maps are used with huge Overlays to track the Troop Movements.

Manual Mapping is an art of showing the real time objects on a piece of paper with a uniq concept located in it.(geography,History,social changes)

CAD (Computer Aided Drafting)CAD (Computer Aided Drafting)

CAD is rooted in drafting—CAD has a great facility for creating and representing geographic features as drawings in a computer

In early graphics systems, the data model was simple and consisted almost entirely of symbolized graphic features

Advantages:• Features were represented by a graphic symbol• Features were stored in a single file format.•Tracking of the data was much easier.

In graphic system software, map files (i.e., layers) can be edited, manipulated, displayed, & generally managed..

Disadvantages:• Features were not so intelligent as today.• The time taken to regenerate the drawing is very high.• Performance of the system is very poor due to graphic size.• Editing of the existing drawing/Map is is very hectic as if one feature is effected in one area then all the feature with the same symbol need to be changed again.

AM/FM a Semi GISAM/FM a Semi GIS

After 1970’s CAD have been implemented in many sectors and was very successful.

However, Large Utility companies and other companies which needed Facility Mapping suffered with the inabilities of CAD systems.

The Concept of facility Mapping has been into the lime lite around mid 70’s.

FM is nothing but CAD but it has its own defined features in it (transformers, repeaters) along with the default text. Some advanced FM systems even provided a data linking facility to the features.

In one word an AM/FM systems is 90% Automated CAD systems with its defined features.

Later on FM has become the stepping stone for GIS

1988 - Indian Remote Sensing Satellite (IRS) system is commissioned with the launch of IRS-1A.

1989 - The National Remote Sensing Agency prepares the first Wasteland Atlas. 

1989 - The National Remote Sensing Agency prepares the first Wasteland Atlas.

1996 -ESRI India is formed.

- Tata Consultancy Services (TCS), India established in 1968, starts with the TCS GIS group to provide services in the areas of GIS, Digital Image Processing, Automated Mapping and Facility Management.

-The Mountain Natural Resource Information Systems (MENRIS),Nepal is established to facilitate the application of GIS and remote sensing ( contd…)

Mile Stones in GIS

1998 - Tata Infotech is appointed as exclusive distributor of MapInfo products in SAARC region.

- Bentley India is established.

- Kampsax India Ltd. a photogrammetry is formed.

- Tele Atlas starts its operation in India.

1999

-The first "GIS Forum South Asia’99" is organised at Nepal.

- Autodesk India Ltd. is formed.

- Landsat 7 carrying Enhanced Thematic Mapper Plus (ETM+) is launched. - IKONOS is launched

Mile Stones in GIS

Trends Trends

Era of Manual Mapping

AMFM\GIS

Desktop GIS

Application GIS

CAD\CAM

Web GIS Mobile GIS

MapObjects

MapX

GeoPbjects

Internet GIS

ArcIMS

MapXtreame

WebMap

MapGuide

Handheld GIS

ArcPAd

MapInfo

SuperGIS

Server Based GIS

Implementing GIS in various DomainsImplementing GIS in various Domains

UtilitiesUtilities Transport & logisticsTransport & logistics CommunicationCommunication Urban planningUrban planning MilitaryMilitary ForestryForestry EnvironmentEnvironment AgricultureAgriculture

List Of some important DomainsList Of some important Domains

What Data is in Your GIS?What Data is in Your GIS?

• What What featuresfeatures do you map? do you map?

• What What attributesattributes do you need to collect data do you need to collect data on?on?

• What What attribute valuesattribute values can you give the can you give the attribute?attribute?

GIS Topology

Node Line (Arc) Area(polygon)

Basic Elements

GIS Topology

Point FeaturesPoint Features

• Points have a single geographic Points have a single geographic coordinate such as:coordinate such as:– TreeTree– Traffic accidentTraffic accident– Lamp postLamp post

Line FeaturesLine Features

• Lines (Arcs) are a series of geographic Lines (Arcs) are a series of geographic coordinates joined to form a line such coordinates joined to form a line such as:as:– RoadRoad– Stream Stream – RailwayRailway

Area FeaturesArea Features

• Areas (Polygons) are a series of Areas (Polygons) are a series of geographic coordinates joined together geographic coordinates joined together to form a boundary such as: to form a boundary such as: – LakeLake– Soil typesSoil types

Geography Data Types and Data Models

Map data. (SPATIAL) Map data contains the location and shape of geographic features. (CartographicCartographic (Map (Map

Data)Data))

Attribute data. Attribute (tabular) data is the descriptive data that GIS links to map features.

Image data. Image data ranges from satellite images and aerial photographs to scanned maps (maps that have been converted from printed to digital format).

Data models for GIS (Spatial Data)

Spatial Data refers to information related to a location anywhere on the earth's surface, and allows users to look at an area or geographic feature in relation to other areas (in relation to changes over time and in relation to various factors)

Data models for GIS (Spatial Data)

SPATIAL DATASPATIAL DATAVector (Object-Based)

Raster (Field-Based)

Object-based model (vector)

Geographic space is populated by discrete and identifiable objects

Discrete Data

Data that can only take certain values.

For example: the number of students in a class (you can't have half a student).

Continuous Data

Data that can take any value (within a range)

Examples: heights. People's heights could be any value (within the range of human heights), not just certain fixed heights.

A discrete object

• Has identifiable boundaries

• Is relevant to some intended application

• Is describable by one of more attributes (characteristics)

Objects

• Exact objects - are generally man-made features with precise boundaries

(e.g. buildings, bridges, etc.)

• Inexact objects - are generally natural

features with transitional, or “fuzzy” boundaries. (rivers, trees, etc.)

Objects are represented as:

• Points

• Lines

• Polygons

Vector Data StructuresVector Data Structures

Vector data files has been Vector data files has been captures as points, lines and captures as points, lines and polygonspolygons- Land cover classes is - Land cover classes is a fine example.a fine example.

Field-based model (raster)

Geographic space is populated by one or more spatial phenomena

Spatial phenomena

Are real-world features that vary continuously over space with no obvious or specific extent and are represented as surfaces

The surfaces in a field-based model can be conceptualized as being composed of:

• Grid cells or pixels– regular tessellations

• Polygons (i.e., triangles)– irregular tessellations

RASTER MODELRASTER MODEL

Spatial data structuresSpatial data structures

Raster data files consists of Raster data files consists of rows of uniform cells coded rows of uniform cells coded according to data vaccording to data values- Land alues- Land cover classes is a fine example.cover classes is a fine example.

ADVANTAGES OF VECTOR MODELADVANTAGES OF VECTOR MODEL

• PRECISE EXPRESSIONPRECISE EXPRESSION• LESS DATA VOLUMELESS DATA VOLUME• FAST RETRIEVALFAST RETRIEVAL• FAST CONVERSIONFAST CONVERSION

ADVANTAGES OF RASTER MODELADVANTAGES OF RASTER MODEL

• SIMPLE DATA STRUCTURESIMPLE DATA STRUCTURE• EASY FOR MODELLINGEASY FOR MODELLING• SUITABLE FOR 3D DISPLAYSUITABLE FOR 3D DISPLAY• INTEGRATION OF IMAGE DATAINTEGRATION OF IMAGE DATA• AUTOMATED DATA CAPTUREAUTOMATED DATA CAPTURE

DISADVANTAGES OF VECTOR MODELDISADVANTAGES OF VECTOR MODEL

• COMPLICATED STRUCTURECOMPLICATED STRUCTURE• DIFFICULTY IN UPDATINGDIFFICULTY IN UPDATING• EXPENSIVE DATA CAPTUREEXPENSIVE DATA CAPTURE

DISADVANTAGES OF RASTER MODELDISADVANTAGES OF RASTER MODEL

• LARGE DATA VOLUMELARGE DATA VOLUME• LOW PRECISIONLOW PRECISION• DIFFICULTY IN NETWORK DIFFICULTY IN NETWORK ANAYLYSISANAYLYSIS• SLOW CONVERSIONSLOW CONVERSION

Attribute Data ModelAttribute Data Model

• Non-Cartographic (Attribute)Non-Cartographic (Attribute)- - descriptive information in a database descriptive information in a database about the cartographic features located about the cartographic features located on a map.on a map.– AttributesAttributes– Attribute ValuesAttribute Values

Tabular ModelTabular Model

Hierarchical ModelHierarchical Model

Relational ModelRelational Model

Network ModelNetwork Model

Object-Oriented ModelObject-Oriented Model

Attribute Model TypesAttribute Model Types

AttributesAttributes can be numeric or alfa can be numeric or alfa numeric data that is assigned to numeric data that is assigned to a point, line or area spatial a point, line or area spatial featuresfeatures

Example Attributes…Example Attributes…

Stand ID, Compartment Stand ID, Compartment no,Vegetation type, Name of the no,Vegetation type, Name of the Forest Block,Type of Road,VSS Forest Block,Type of Road,VSS code etc.,code etc.,

AttributesAttributes

AttributesAttributes

Description or characteristic of a featureDescription or characteristic of a feature

• Possible attributes for the feature TreePossible attributes for the feature Tree– HeightHeight– DiameterDiameter– SpeciesSpecies– ConditionCondition– AgeAge

Attribute ValuesAttribute Values

The value given to an attributeThe value given to an attribute

• Possible Possible valuesvalues for the attributes of a Tree for the attributes of a Tree featurefeature– HeightHeight = 15m= 15m– DiameterDiameter = 0.75m= 0.75m– SpeciesSpecies = Oak= Oak– ConditionCondition = Good= Good– AgeAge = 8 years= 8 years

Types of Attribute ValuesTypes of Attribute ValuesThere are a number of different types ofThere are a number of different types ofattribute valuesattribute values

Feature Attribute Attribute Values

Character Pole Pole ID ABC123

Numeric Pole Height 15m

Menu Pole Condition GoodAveragePoor

Date Pole Date User generatedAuto generated

Time Pole Time User generatedAuto generated

Data Quality

• “fitness for use”• varies with

– intended use– scale– method of collection

Measures of data quality

• reliability• accuracy• relevance• timeliness• intelligibility

• completeness• known precision• concise• convenience• integrity

More considerations

• projection

• scale

• classification scheme

• cartographic quality

• metadata

• transfer format

Accuracy

• how closely the data represent the real world

• limited by– data collection equipment and technique– intended use– cost

Precision

• exactness of representation• numerical data

– number of significant digits

• categorical data– level of detail– number of categories

Error

• deviation, variation, & discrepancy

• lack of accuracy & precision

• types– systematic– random

Error Sources

• original source material

• data collection

• data automation and compilation

• data processing and analysis

• inherent & operational

Uncertainty

• degree of doubt

• accuracy and precision are not known

• error is not known (but may be large)

• greater when data from multiple sources & scales are mixed

Components of data quality

• lineage (data history)• positional accuracy

– “one line width”– varies with scale– tables

• attribute accuracy– numerical– categorical

Components of data quality

• logical consistency– with real world– within model & system– between data sets & files

• boundary errors• layering errors

• completeness– spatial– thematic

Components of data quality

• temporal accuracy– precision of temporal measurements– age of data

• semantic accuracy– labeling

Assessment of data quality

• positional accuracy– random sample– root mean square

error (RMSE)– examine results for

patterns & concentrations

• attribute accuracy– random sample– error matrix– errors of inclusion &

exclusion– percent correctly

classified

Data Capture SourcesData Capture Sources

• Digitizing from paper mapsDigitizing from paper maps

• ScanningScanning

• Traditional surveying techniquesTraditional surveying techniques

• Paper records & field notesPaper records & field notes

• PhotogrammetryPhotogrammetry

• Remote sensingRemote sensing

• GPSGPS

GIS Data StorageGIS Data Storage

• CartographicCartographic (Map Data)- observations on (Map Data)- observations on spatially distributed features, activities, or spatially distributed features, activities, or events, which are definable as:events, which are definable as:– PointsPoints– Lines (Arcs)Lines (Arcs)– Areas (Polygons)Areas (Polygons)

GIS Data StorageGIS Data Storage

• Non-Cartographic (Attribute)Non-Cartographic (Attribute)- - descriptive information in a database descriptive information in a database about the cartographic features located about the cartographic features located on a map.on a map.– AttributesAttributes– Attribute ValuesAttribute Values