introduction to geographical information systems

8/7/2019 Introduction to Geographical Information Systems.

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GIS

Sandeep Kumar Jakkaraju


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Disclaimer:

I dont claim to be a GURU in this subject ratherI think Iam a student. But I expect the audience of thispresentation to at least have a vague idea about the

below mentioned terms.

Data, Information, Computer, System, InformationSystems, Databases, RDBMS, Spatial, dimensions, 1D,2D, 3D, Cartesian Coordinate System, Point, Line,Polygon, B-Trees, Topology, Metadata, RadialDistance, Ontology, Geodesy, Earth, Physics,Geophysics, Astrophysics and Metaphysics.


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What is GIS ?


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Geographic Information System

Geographical InformationSystem

Geographical InformationScience


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Concepts and Techniques ofGeographicInformation Systems by C.P.Lo and AlbertYeung

GIS is a set of computer-based systems formanaging geographic data and using these datato solve spatial problems. Some people call itSpatial Information System as well.


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Geographic / Spatial Data (multidimensionality).

Cartographic application.

Spatial Database.

Information Systems and Analysis Tool.


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Problem:

Find the nearest Bank ATM from our office building.

A problem in Topology ?A problem of ordering of 2D points in space ?A spatial analysis problem.


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GIS is about spatial data, Information System,Cartographic application, and spatial analysis tool.

Some people even call them as Spatial DecisionSupport Systems (SDSS).


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Problem

Find the route between two locations in a city.

A problem in Graph Theory ?

A problem in Operations Research ?

A spatial analysis problem.


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The website of MapQuest orRouteGURU is an

example of a web-based spatial decision supportsystem which solves this problem.


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GIS


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So GIS also includes the people using it !


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Maps and GIS

GIS as a Cartographic Application


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Map

Map

Mental image ofreality

Reality

Map user

Cartographer / GIS

specialist

Compile Imagine

RecognizeSelectClassifySimplify

Symbolize

ReadAnalyzeInterpret

Map


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Map ScaleThe scale of a map is the ratio or proportion betweenthe distances measured on the map and thecorresponding distances measured on the ground.

You can do the mathematics.


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Large scale Small scale

1:500 1:24000

1:2500001:24000

Map Scale


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lasses of Maps

1) General Purpose orReference maps:

hese are maps not designed for any specific applications. This class of mapsocus on locations and shows a variety of physical and cultural features such asrainage, roads, railways, airports, forest and cultivate areas etc. They serve ashe base maps for developing and integrating other form of geographicinformation.

) Special Purpose or Thematic maps:

hese maps are designed to depict a particular type of feature or measurementnly. Like it can show the variation of rainfall across certain region. These mapsre generated using the base maps.


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Shape of Planet Earth?

Datum is a set of referencepoints on the earth's surface against whichposition measurements are

made,andan associated model of the shape of the earth to define ageographic coordinate system.

Horizontal datums are used fordescribingapoint on the earth's surface, in latitude and longitudeVertical datums measure elevations ordepths


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Coordinate Systems

Cartesian coordinate system Geographic coordinate system

X

Y

- X

+Y

- X

- Y

+X- Y

+X+Y

The linepassing through the (former) Royal Observatory, Greenwich is the zero-longitude reference line.Greenwich Meridian.

Equator is the line at Zero degree latitude.


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I am assuming t=to in this problem also for time being !


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Semi-Major AxisSemi Minor Axis

Flattening

Latitude is vertical angle

Longitude is the horizontal angle.


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Map Projection

A mapprojection is a systematic representationofall part of the surface ofa round body

especially earth on aplane.


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ShapeScaleArea

DirectionDistance

Represent the two-dimensional curvedsurface of the earth on aplane

Mapprojections can be constructed to preserve oneor some of these properties, though not all of them

simultaneously.

Projection systems


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For an application like

MapQuest/RouteGURUTM you would needa map projection that would preserve the

distance as it involves distance basedcalculations for finding the shortest route.


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TIP

As faras projections is concernedjust make

sure that all the layers you overlay are in thesame projection


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Sources of

Spatial Data

Spatial data for the general purpose andreference maps for GISare collected using the

methods of land surveying, aerial and satellitephotgrammetry andglobal positioning system(GPS)


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Global PositioningSystem


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Attribute or NonSpatial Data

The Non-Spatial data can be collected usingmethods like surveys, census etc. which can be

used for thematic mapping.


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Real world

Digital Representation of Geographic Data


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Digital Representation of Geographic DataContd.

The real-world features exists in two different forms objects

andphenomenon.

Objects are discrete anddefinite hence can be representedusingpoint or line orpolygon which is Vector Format.

Phenomenon is distributed overa large area such has

elevation or climate etc. which is represented in Raster

Format.


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Digital Representation ofGeographic Data

Components

Point

Line

Polygon

X,Y

Rows

Columns

Raster Format

X,Y

X,Y X,Y X,Y

Vector Format

Geometry

Attributes

Data


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Other topics Digitization (Vector Data Creation)

Spatial OperationsContains, Overlaps, Intersects, etc

Spatial Analysis on Vector DataOverlay, Buffering, NetworkAnalysis, etc Data Quality andStandards Challenges forLBSapplications.


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Open Source GIS UMN-Mapserver

(Opensource mapping server for web-based GIS

applications. Mainly in PhpMapscript)

QuantumGIS

(Automatic creation ofMap File)

OpenMap API

(Open Source Mapping API in Java)

PostGIS

(Spatial Extension to PostgreSQL)Similar to ORACLE Spatial.


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Did you see the tip of the Iceberg ?

Thankyou!


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References:

[1].

[2].[3].


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Any Questions?

introduction to geographical information systems

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