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Principles of Geographic InformationSystems

GeES 332

Introduction to GeographicInformation Systems

Presented by:Daniel Alemayehu

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Chapter One Outline 1.1 Definition

1.1.1 GIS is a toolbox

1.1.2 GIS is an Information System

1.1.3 GIS is an approach to Science

1.1.4 GIS plays a role in the society

1.2 History or Evolution of GIS

1.2.1 Computer Mapping (Beginning Years,

1970s) 1.2.2 Spatial-database management (Adolescent

Years, 1980s)

1.2.3 Map Analysis and Modeling (Maturing Years,1990s)

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1.3 GIS Application 1.4 Components of GIS 1.4.1 Hardware 1.4.2 Software 1.4.3 Data 1.4.4 Live Ware or Analyst

1.4.5 Procedures or Methods 1.5 Capabilities of GIS 1.5.1 Data Capture 1.5.2 Data Storage

1.5.3 Data Management 1.5.4 Data Retrieval 1.5.5 Data Analysis 1.5.6 Data Display

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Definition

There is no clear-cut definition for GIS.

Different people defined GIS according tocapability and purposes for which it is

applied.

A typical GIS can be understood by the helpof various definitions given below:

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GIS is a toolbox

A GIS can be seen as a set of tools foranalyzing spatial data.

one definition of a GIS is the software in thebox that gives us the geographiccapabilities we need.

Peter Burrough, in his pioneering textbook,defined GIS as a powerful set of tools for

storing and retrieving at will, transformingand displaying spatial data from the realworld for a particular set of purposes(Burrough, 1986).

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The key word in this definition is Powerful.

Burroughs definition implies that GIS is a

tool for geographic analysis.

This is often called the toolbox definition ofGIS because it stresses a set of tools eachdesigned to solve specific problems.

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GIS is an Information System

Jack Estes and Jeffrey Star defined a GISas an information system that is designedto work with data referenced by spatial or

geographic coordinates. In other words, a GIS is both a database

system with specific capabilities forspatially-referenced data, as well as a set ofoperations for working with the data (Starand Estes, 1990)

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Another information systemdefinition of a GIS

In 1979 during the infancy of the technology, KenDueker defined a GIS as a special case of

information systems where the database consists

of observation on spatially distributed features,activities or events, which are definable in spaceas points, lines or areas.

A geographic information system manipulates

data about these points, lines, and areas toretrieve data for ad hoc queries and analyses

(Dueker, 1979).

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GIS is an approach to Science

Goodchild defined geographic informationscienceas the generic issues that surround theuse of GIS technology, impede its successfulimplementation, or emerge from theunderstanding of its potential capabilities.

He also noted that this involved both research onGIS and research with GIS.

Supporting the science are the uniqueness of

geographic data, a distinct set of pertinentresearch questions that can only be askedgeographically, the commonality of interest ofGIS meetings, and a supply of books and

journals.

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GIS plays a role in the society

Nick Chrisman (1990) has defined GIS as

organized activity by which people

measure and represent geographic

phenomena then transform theserepresentations into other form while

interacting with social structures.

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This definition has emerged from an areas

of GIS research that the examined howGIS fits into society as a whole, including

its institutions and organizations, and howGIS can be used in decision making,especially in a public setting such as a

town meeting, or on a community groupWeb site.

This latter field is termed PPGIS, for public

participation GIS.

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History or Evolution of GIS

Manual GIS systems evolved from the discipline ofcartography, where architects or site designersneeded to visually compare the building plan with

the site survey. In the early 1950s, where geographers and

transportation engineers developed quantitativemethods for analyzing transportation study data.

The history of GIS dates back 1960 wherecomputer based GIS have been used.

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A sound and stable data structures tostore and analyze map data becamedominant in the early 1970s.

Another significant breaks throughoccurred with the introduction and spreadof personal computers in 1980s

In the 1990s, GIS has matured somewhat,with research directed away from the basicissues of map production and encoding,which have been solved after a fashion.

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Computer Mapping(Beginning Years,1970s)

The early 1970's saw computer mapping

automate map drafting. The points, linesand areas defining geographic features on

a map are represented as an organized setof X,Y coordinates.

The pioneering work during this period

established many of the underlyingconcepts and procedures of modern GIStechnology.

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Spatial-database management(Adolescent Years,1980s)

During 1980's, the change in data format andcomputer environment was exploited. Spatialdatabase management systems were

developed that linked computer mappingcapabilities with traditional databasemanagement capabilities.

In these systems, identification numbers areassigned to each geographic feature

Early in the development of GIS, twoalternative data structures for encoding maps

were debated.

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Vector Data Model & Raster Data Model

By the mid-1980's, the general consensuswithin the GIS community was that thenature of the data and the processingdesired determines the appropriate datastructure.

This realization of the duality of mappeddata structure had significant impact ongeographic information systems.

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Vector and Raster models

Vector Raster

Vector

models- points,lines,polygons

- more complexobjects

Rastermodels- grid cell

Real World

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Map Analysis and Modeling(Maturing Years,1990s)

As GIS continued its evolution, theemphasis turned from descriptive query toprescriptive analysis of maps.

Digital representation, on the other hand,makes a wealth of quantitative (as well asqualitative) processing possible.

The application of this new theory tomapping was revolutionary and itsapplication takes two formsspatialstatistics and spatial analysis.

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Meteorologists and geophysicists have usedspatial statistics for decades to characterize thegeographic distribution, or pattern, of mapped

data. Spatial analysis applications, on the other hand,

involve context-based processing. For example,foresters can characterize timber supply by

considering the relative skidding and log-haulingaccessibility of harvesting parcels.

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GIS Application What do we do with GIS?

Master Planning Site development planning; Site management. Suitability Analysis: Screening & Potential

Development site selection; Suitable Site Selection; Resource Potential; Land Use Plans. Natural Resources Management Habitat Analysis; Forest Management;

Land Conservation; Production/extraction anal sis

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Other Disciplines

Defense/Homeland Security;

Real Estate and Site Selection;

Health Care Management and Planning;

Epidemiology;

Archaeology;

Conservation/Land Management (Global,national, regional local);

Any other discipline that operates in or

studies phenomena across time and space.

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Components of GIS

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Hardware

The general hardware components of

Geographic Information System are themain computer system or the Central

Processing Unit (CPU), the terminal,keyboard and the visual display unit(VDU), digitizer, disk drive, plotter, printer

etc.

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Hardwares

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GIS Hardware-CPUs

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Creating graphic data for GIS

applications

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Large format plotters

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Software

The GIS software is used to carry out the

GIS operations. These are required fordriving the hardware. Common interfaces in

GIS are menus, graphical icons andcommands.

Most Common GIS Software available in

the market are: ESRI products like Arc/Info,Arcview, ArcGIS, Map Info from MapInformatics Inc, Intergraph, IDRISI etc.

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All packages must be capable of data input,storage, management, transformation,

analysis, and output, but the appearance,methods, resources, and ease of use of thevarious systems may be very different.

Todays software packages are capable ofallowing both graphical and descriptive datato be stored in a single database, known asthe object-relational model.

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MapInfo

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Arc/Info

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ArcView

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IDRISI

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Data

Includes both spatial and non-spatial dataon which GIS operations are performed toderive new information. Spatial data from

various sources such as Remote sensingimages, Aerial Photographs or Map Datacan be integrated with corresponding non-spatial data in GIS.

Perhaps the most time consuming andcostly aspect of initiating a GIS is creatinga database.

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Live Ware or Analyst

Equally important as the computer hardware andsoftware, the brain ware refers to the purposeand objectives, and provides the reason and

justification, for using GIS. The people are the component who actually

makes the GIS work. They include a plethora ofpositions including GIS managers, database

administrators, application specialists, systemsanalysts, and programmers.

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Procedures or Methods

Procedures include howthe data will be

retrieved, input into the system, stored,managed, transformed, analyzed, and

finally presented in a final output.

The procedures are the steps taken toanswer the question need to be resolved.

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Capabilities of GIS

A GIS is often defined not for what is but

for what it can do.

This functional definition of GIS is veryrevealing about GIS use, because it showsus the set of capabilities that a GIS isexpected to have.

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Data Capture

Getting the mapinto the computer is a critical firststep in GIS. Geocoding must include at least theinput of scanned or digitized maps in some

appropriate format. The system should be able to absorb data in a

variety of formats, not just in the native format ofthe particular GIS. For example, an outline map

may be available as an Auto CAD DXF format file. The GIS should at a minimum be capable of

absorbing the DXF file without further modification.

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Data Storage

Data storage within a GIS has historicallybeen an issue of both spaceusually howmuch disk space the system requires and

access, or how flexible a GIS is in terms ofmaking the data available for use.

The massive reductions in the cost diskstorage, new high-density storage mediasuch as the CD-ROM, and the integration ofcompression method into common operatingsystems have made the former less critical

and the latter more so.

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Current emphasis, therefore, is upon

factors that improve data access.

This has been a consequence also of therise of distributed processing, the Internet,and the World Wide Web.

As a result, many GIS packages are now

capable of using metadata, or data aboutdata,in an integrated manner.

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Data Management

Much of the power of GIS software comes fromthe ability to manage not just map data but alsoattribute data.

Every GIS is built around the softwarecapabilities of a database management system(DBMS), a suite of software capable of storing,retrieving selectively, and reorganizing attributeinformation.

The database manager allows us to think that allthe data are available, that the data arestructured in a simple flat-file format and thatthey constitute a single entity.

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In fact, the database manager may havepartitioned the data between files andmemory locations and may have structured

it in any one of several formats and physicaldata models.

A database manager is capable of manyfunctions. Typically, a DBMS allows dataentry, and data editing, and it supportstabular and other list types of output,sometimes independent of the GIS.

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Data Retrieval

Another major area of GIS functionality isthat of data retrieval.

A GIS supports the retrieval of features by

both their attributes and their spatialcharacteristics.

All GIS systems allow users to retrieve

data. Nevertheless, among systems somemajor differences exist between the typeand sophistication of GIS functionality fordata retrieval.

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The most basic act of data retrieval for aGIS is to show the position of a single

feature. This can be by retrieving coordinates as

though they were attributes, or more

commonly by displaying a feature in itsspatial context on a map with respect to agrid or other features.

GIS allow a set of retrieval operationsbased on using one or more map featuresas handles to select attributes of those

features.

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Buffering allows the GIS users to retrieve

features that lie within perhaps 1 mile of anaddress, within 1 kilometer of a river, or

within 500 meters of a lake. Similarly, weighted buffering allows us to

choose a non uniform weighting of features

within the buffer, favoring close-by insteadof distant points, for example.

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Distance Buffers

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Data Analysis The analysis capabilities of GIS systems vary

remarkably.

Among the multitude of features that GISsystems offer are the computation of the slope

and direction of slope (aspect) on a surfacesuch as terrain; interpolation of missing orintermediate values; line-of-sight calculationson a surface; the incorporation of specialbreak or skeleton computations necessary tocalculate the amount of material that must bemoved during cut-and-fill operations such as

road construction.

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Almost unique to GIS, and entirely absentin other types of information systems, aregeometric tests.

These are described by their dimensions,point-in-polygon, line-in-polygon, andpoint-to-line distance.

point-in-polygon, is how a point databasesuch as a geo coded set of point samplesis referenced into regions.

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Thus a set of location for soil samples,

generated at random, could be point-in-polygon merged with a digitized set of district

boundaries so that a sample list can be sent toeach soil district manager.

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Data Display GIS system need to be able to perform what has

become called desktop mapping.

GIS typically can create several types of thematicmapping, including choropleth and proportional

symbol maps; and they can draw isoline and cross-sectional diagrams when the data are threedimensional.

Almost all GIS packages now either allowinteractive modification of map elements movingand resizing titles and legends or allow theiroutput to be exported into a package that has these