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# Introduction to Geographical Information Systems.

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## Content

GIS Sandeep Kumar Jakkaraju

Disclaimer: I don¶t claim to be a GURU in this subject rather I think I am a student. But I expect the audience of this presentation to at least have a vague idea about the below mentioned terms.

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

What

is GIS ?

Geographic Information System Geographical Information System Geographical Information Science

³Concepts

and Techniques of G of  Geographic by C.P.Lo and Albert Information Systems Systems by Yeung´ GIS is a set of computer-based systems for  managing geographic data and using these data to solve spatial problems. Some people call it Spatial Information System System as well.

Geographic / Spatial Data (multidimensionality ). ).

Cartographic Cartograph ic application.

Spatial Database.

Information Systems and Anal Analysis Tool.

Problem: Find the nearest Bank ATM from our office building.  A problem in Topology Topolog y ?  A problem of ordering of 2D points in space ?  A spatial analy anal ysis problem.

GIS is about spatial data, Information Sy System, stem, Cartographic application, and spatial anal ysis tool. Some people even call them as Spatial Decision Support Su pport Systems (S (SDSS).

Problem

Find the route between two locations in a cit y.  A problem in Graph Theor y ?  A problem in Operations Research ?  A spatial anal ysis problem.

The website of MapQuest or R or RouteGURU outeGURU is an example of a web-based spatial decision support system which solves this problem.

GIS

So GIS also includes the people using it !

Maps and GIS GIS as a Cartographic Application

Cartographer / GIS GIS specialist

Recognize Select Classify Simplify Symbolize

Reality

Map

Compile

Imagine Map

Mental

image of  reality

user

Map

Map Scale The scale of a map is the ratio or proportion between the distances measured on the map and the corresponding corresponding distances measured on the ground. You can do the mathematics. m athematics.

Map

Scale

1:500

1:24000

Large scale

1:24000

1:250000

Small scale

lasses of Maps 1) General Purpose or R or Reference maps: maps: hese are maps not designed for any any specific applications. This class of maps ocus on locations and shows a variety variety of phy physical and cultural features such as rainage, roads, railway railways, airports, forest and cultivate areas etc. They They serve as he base maps for developing and integrating other form of geographic information. ) Special Purpose or Thematic maps: maps: hese maps are designed to depict a particular ty type of feature or measurement nly nly. Like it can show the variation of rainfall across certain region. These maps re generated using the base maps.

Shape of Planet Earth?

Datum is a set of reference p reference  points oints on the ea earth's surf ace aga against inst which p which  position osition mea measurements are mad ade, e, and an associ ssociaate ted d mo mod del of the shap shapee of the ea earth to define a geo eog gr aphic aphic coor din inaate system. Horizontaal da Horizont datums tums are used used for  for d describin escribing g a  p  point oint on the ea earth's surf ace, in la latitu titud de and lon long gitu itud de Verticaal da Vertic datums tums mea measure eleva elevations or d or de p  pths ths

Coordinate Systems

Cartesian coordinate sy system

Geographic coordinate sy system

Y -X +  Y

+X +  Y X

-X -Y

The

+X -Y

line  passin line pa ssing g throu throug gh the (former) Roya Royal Observa Observatory, Greenwich is the zero-long zero-longitu itud de reference line. Greenwich Meri erid dian. Equaator is the line at Zero degree la Equ latitu titud de.

I

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

Semi-Maj emi-Major or Axis Semi

Minor Axis Fla Flattening ttening

Latitud Latitu de is vertica vertical angle Lon ong gitu itud de is the horizonta horizontal angle.

Map

Projection

ap p  pro  jection A map ro j ection is a system systemaatic re p re present resentaation of aall of  ll pa  part rt of the surf ace of a of a roun round d bo bod dy es p  peci eciaally ea earth on a  p  pllane.

Projection systems Re p  present resent the twotwo-d dimension imensionaal curve curved d surf ace of the earth on a  p  pllane

Shape Scale  Area Direction Distance

Map p Map  pro ro jections  jections ca can be constructed constructed to p to  preserve reserve one or some of these p these  pro ro perties,  perties, thoug though not all of them simulta simultaneously.

For an application like MapQuest/R MapQuest/ outeGURU Route GURUTM you would need a map projection that would preserve the distance as it involves distance based calculations for finding the shortest route.

TIP

As f ar  r aas  p  pro ro j  jections ections is concerned concerned  j  just ust mak  mak e sure tha that all the la layers you overla overlay are in the same me p  pro ro j  jection ection

Sources S pa  pati tiaal

of S pa  pati tiaal Da Data

data for the gener al  p dat  pur  ur  p  pose ose and reference map mapss for GIS are collected collected usin using g the method metho ds of la land surveyin surveying g, aeri eriaal and satellite  phot  p hotg gr ammetry and glob lobaal  p  positionin ositioning g system (GPS)

Globa Global Positioning ositioning System

Attribute or Non S pa  pati tiaal Da Data The

Non-S pa  pati tiaal da datta can be collected collected usin using g method metho ds lik  lik e surveys, census etc. which ca c an be used use d for thema thematic mapp mappin ing g.

Dig Di git itaal Re p Re present resentaation of Geog Geogr aphic aphic Da Data

Real world

Dig Di git itaal Re p  present resentaation of Geog Geogr aphic aphic Da Data Contd. d fe reaal-worl re l-world feaatures exists in two different forms ob j ob jects ects and  p  phenomenon. henomenon. The

Ob j  jects ects are discrete and definite hence ca can be re p re presente resented d using usin g  p  point oint or line or  p or  poly olyg gon which is Vector Format. Phenomenon

is distribute istributed d over  over aa lar ge are reaa such ha h as elevaation or clima elev climate etc. which is re p re presente resented d in Raster Format.

Digital Representation of Geographic Data Components

Vector Format

X,Y

X,Y

X,Y

Point X,Y

Line

Raster Format

Rows

X,Y

Polygon

Columns

Data

Attributes Geometry

Other to p to pics ics  Dig Digitiz itizaation (Vector Da Data Cre Creaation)  S pa  pati tiaal O p O per  er ations Contaains, Overlap Cont Overlaps, s, Intersects, etc

 S pati  patiaal An Anaalysis on Vector Da Data Overlaay, Buffering Overl Buffering, Networ k An k  Anaalysis, etc

 Data Qu Quaality and Standa dar  r ds  Ch Chaallen lleng ges for L for LBS app applic licaations.

Open Source GIS  UMN-Mapserver (O p  pensource ensource mapp mappin ing g server for web-ba web-base sed d GIS applic app licaations. Ma Mainly inly in Ph p Map Mapscri scri p  pt) t) QuantumG IS (Automaatic crea (Autom creation of Map of Map File) OpenMap API (O p  pen en Source Mapp Mappin ing g API in Ja Java)  PostGIS (S pa  pati tiaal Extension to Post ostg greSQL) Simil imilaar to ORACL ORACLE S pa  pati tiaal.

Did Di d you see the ti p ti p of the Iceber g ?

Thank  you!

References: [1]. [2]. [3].

Any Questions?

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