INTRODUCTION TO GIS

Geographic + Information + System

Knowledge of proper geographic location is an important aspect in this technically advanced and competitive market.

Information is the result of processing, manipulating and organizing data in a way that adds to the knowledge of the person receiving it.

A collection of entities organized in a manner to cooperate with each other in order to accomplish a common objective.

GIS or Geographical Information Systems is broadly a computer capable of assembling, storing, manipulating and displaying geographically referenced information. Practitioners also regard the total GIS as including personal and the data that go into the system.

Defining GIS is a tough task though not an impossible one. This is more evident from the following definitions.

GIS is …

… a system for capturing, storing, checking, integrating, manipulating, analysing and displaying data which are specifically referenced to the earth.(Charley 1987)

GIS is …

… an information technology which stores, analyses and displays both spatial and non-spatial data.(Parker 1988)

…an institutional entity, reflecting an organisational structure that integrates technology with a database, expertise and continuing financial support over time. (Carter 1989)

… an information system that is designed to work with data referenced by spatial or geographic coordinates. A GIS is thus both a database system with specific capabilities for spatially referenced data as well as a set of operations for working with data. (Star & Estes 1990)

… a system of computer software and procedures designed to support the capture, management, manipulation, analysis and display of spatially referenced data for solving complex planning and management problems.

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So.. What’s a GIS?So.. What’s a GIS?

...a computer based system to capture, store, edit,manipulate, analyze, synthesize and display

geographically referenced information

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...a computer system capable of visualizing data which describe places on the earth’s surface

Digital data is expressed as numbers

GIS defined...

GIS converts digital data into maps

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With GIS you can do more than just view maps, youcan also query and analyze map layers simultaneously

GIS defined...

Many professionals, such as foresters, Army, urban planners, and geologists, have recognized the importance of spatial dimensions in organising & analysing information. Whether a discipline is concerned with the very practical aspects of business, or is concerned with purely academic research, geographic information system can introduce a perspective, which can provide valuable insights as 70% of the information has geographic location as it's denominator making spatial analysis an essential tool.

*Ability to assimilate divergent sources of data both spatial and non-spatial (attribute data)

*Visualization Impact *Analytical Capability *Sharing of Information

Need of GIS?

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GIS FunctionsGIS Functions► Input:Input: adding data or creating new data adding data or creating new data► ManipulationManipulation: updating or reformatting data: updating or reformatting data► Query:Query: two methods - query the database (tabular two methods - query the database (tabular

data) or query the geographic features (spatial data)data) or query the geographic features (spatial data)► Analysis:Analysis: combining multiple types of data over an combining multiple types of data over an

area to answer questions or to develop scenarios area to answer questions or to develop scenarios about that areaabout that area

► Visualization:Visualization: creating 2D maps or 3D creating 2D maps or 3D representationsrepresentations

► Management:Management: spatial spatial andand tabular data tabular data

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Questions a GIS can Questions a GIS can answer...answer...

► LocationLocation Where is it?Where is it?

► ConditionCondition What is at... ?What is at... ?

► TrendsTrends What has changed since... ?What has changed since... ?

► PatternsPatterns What spatial patterns exist?What spatial patterns exist?

► ModelingModeling What if... ?What if... ?

continued...

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Questions a GIS can Questions a GIS can answer...answer...

► ProximityProximity What are the What are the characteristics characteristics of the of the area around existing area around existing

features?features?

► Boundary OperationsBoundary Operations What exists within a What exists within a specific specific region?region?

► Logical OperationsLogical Operations What is unique about a What is unique about a region region or set of features?or set of features?

WHAT DOES GIS DO

1. Collect, store, organise and distribute data

2. Criteria matching: Select a suitable site for picnic that is:

on public land;

with gentle slope;

amongst shaded trees;

within 50 m of canoe-able river

A restaurant within 200 m.

3. Allows exploration of relationships among data layers:

How does population density relate to water availability

High yielding Poplar grows on which soil type

… contd.

4. Allows scenario testing:

If we raise smoke chimney to 1000 feet, will it go out of the adjacent village

If we make the proposed sewage path, will it cut the roads

5. Serve as a data handler for other analyst:

Passing water quality and water-table data to groundwater flow model

Passing geological and topographic data to soil erosion modeler.

6. Aids Visualisation:

It improves understanding and pattern recognition

Facilitates public participation in alternative scenario

Coordinates group decision making

BUT THE GIS IS NOTBUT THE GIS IS NOT

►East to useEast to use► Just a drafting (CAD) program, it needs Just a drafting (CAD) program, it needs

analytical capabilitiesanalytical capabilities►Able to make decisions- That is the job Able to make decisions- That is the job

of the user/interpreterof the user/interpreter►Free of field workFree of field work►Cheep in terms of human resources, Cheep in terms of human resources,

computer resources and data acquisitioncomputer resources and data acquisition

Characteristics of Characteristics of DisciplinesDisciplines

Sample DisciplinesSample Disciplines

1.Development Of Spatial 1.Development Of Spatial Concepts Concepts

2.Means For Capturing And 2.Means For Capturing And Processing Spatial Data Processing Spatial Data

3.Formal And Theoretical 3.Formal And Theoretical FoundationFoundation

4.Applications 4.Applications

5.Supports5.Supports

Geography; Geography; Linguistics ;Psychology; Linguistics ;Psychology; Cognitive Sciences. Cognitive Sciences.

Remote Sensing; Surveying; Remote Sensing; Surveying; Engineering; Cartography; Engineering; Cartography; Photogrammetry .Photogrammetry .

Computer Science; Expert Computer Science; Expert System; Mathematics; System; Mathematics; Statistics. Statistics.

Archaeology; Architecture; Archaeology; Architecture; Forestry; Geo-Sciences; Forestry; Geo-Sciences; Regional & Urban Planning; Regional & Urban Planning; Surveying .Surveying .

Legal Sciences; EconomyLegal Sciences; Economy

Spatial Data handling involves different disciplines

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Components of a GIS

Modeling the Real World

Hardware/

Software

Data andInformation

Results andApplications

HardwareHardware Model Personnel Computers; High Model Personnel Computers; High Performance Workstations; Performance Workstations; Minicomputers; Mainframe Computers.Minicomputers; Mainframe Computers.

Input Devices:Input Devices: Scanners, Digitizers, Scanners, Digitizers, Tape drivers, CD, Keyboard, Monitor Tape drivers, CD, Keyboard, Monitor

Output DevicesOutput Devices :Plotters, Printers :Plotters, Printers

SoftwareSoftware Input Modules ; Editing; MRP Input Modules ; Editing; MRP Manipulation/Analysis Modules; Manipulation/Analysis Modules; Modelling CapabilityModelling Capability

DataData Attribute Data; Remote Sensing Data; Attribute Data; Remote Sensing Data; Spatial Data; Global DatabaseSpatial Data; Global Database

Live WareLive Ware People responsible for digitizing, People responsible for digitizing, implementing using GIS. implementing using GIS.

ELEMENTS OF GIS

Elements of GIS Details

Cartographic Perception :

Which focuses on the map aspects of GIS. Supporters of this view see GIS as a map processing and display system where each map is represented as a layer, mostly in raster format, and is manipulated by a set of map arithmetic functions.

•Database Perception :

emphasizing the importance of a well designed and implemented database. A sophisticated database management system (DBMS) is an integral part of such systems. This view is predominant amongst the GIS community who have computer science background. Application around querying, transaction, processing, large area active database maintenance, map production etc. are suited to this approach.

There are three basic perceptions prevalent in the GIS community

Spatial Integration Perception :

emphasizing the spatial analysis capabilities of GIS. This view focuses on integrated analysis and modeling and seen more as a spatial information science than a technology. It is towards this perception that GIS of present day are developing and is likely to become most widely accepted by the GIS community.

DATA IN GIS

Broadly classified into following categories :

1. Spatial data

2. Non-spatial data

Spatial data :

Spatial data has physical dimensions and geographic locations on the surface of earth. Maps are used to graphically represent geographic features of the earth. A map conveys :

- Positional information about the location on the surface of earth

- Spatial relationship such as adjacent to located within etc.

- Measurable quantities such as length, area, latitude, longitude etc.

Non-Spatial data :

Data that qualifies the spatial data. It is quantitative data expressed as names, numbers, dates, values etc.

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Data Models Data Models and Feature Typesand Feature Types

►VectorVector Points, Lines Points, Lines

and Areasand Areas

►RasterRaster cell matrixcell matrix

Y

X

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Types of Data Models - how do you represent the real world in a computer?

Raster Data ModelCell or Grid MatrixContinuous Data

Vector Data ModelPoints, Lines, PolygonsDiscrete Data

Real World

DATA MODELS

Raster Data Structure (Cartographic Map Model )

The simplest raster data structures consist of an array of grid cells (sometimes termed pixels). Each grid cell is referenced by a row and column number and it contains a number representing the type or value of the attribute being mapped. In raster structures a point is represented by a single grid cell; a line by a number of neighboring cells strung out in a given direction and an area by an agglomeration of neighboring cells.

Raster:

A set of cells located by coordinate is used, each cell is independently addressed with the value of an attribute. •One set of cell and associated value is a LAYER. •It is simple with which spatial analysis is easier and faster. •Requires a huge volume of data to be stored, fitness of data limited by cell size .

Vector representation (Georelational Model)

Vector representation of an object is an attempt to represent it as exactly as possible.

Advantages:

Good representation of phenomenological data structure

Compact data structureTopology can be completely described with

network linkages.Accurate graphicRetrieval, updating and generalization of

graphic and attributes are possible.

Vector•Uses line segments or points represented by their explicit (X,Y) coordinates to identify locations •Discrete objects are formed by connecting line segments which area is defined by set of line segments. •It requires less storage space, outputs are appreciable, estimation of area/perimeter is accurate and editing is faster and convenient. •Spatial analysis is difficult with respect to writing the software program.

CONCEPTS IN GIS

Three basic spatial features can be identified :

Points

Lines

Polygons

Points:

Point locations are used in geography in two ways. The first way is shorthand reference for an area so that a map might show the locations of towns as a scatter of points. The second is as a precise locational reference. For example, the site at which certain measurements are made.

Lines:

Individual points can be joined together to form a second type of spatial feature, a line. Minimum number of points needed to define a line over a short distance is two, in which case the line is necessarily straight. However if more than two points are used, line may be curved and the path of the line between individual points area called segments. Start and end points of a line and the point at which three or more lines join are called nodes.

Polygons:

When a series of lines form an enclosing boundary they create the third type of spatial feature – an area or a polygon. In this case, the number of pairs of x and y coordinates are variable since it depends on the number of lines and number of segments.

RASTER vs VECTOR

Raster representation: Set of cells located by coordinates, each cell is independently addressed with the value of an attribute.

Advantages:-Simple data structures.-The overlay and combination of mapped data

with remotely sensed data is easy.-Various kind of spatial analysis is easy.-Simulation is easy because each spatial unit

has the same size and shape.

Disadvantages:Volumes of graphic data.

The vector model is extremely useful for describing Discrete features, but less useful for describing continuously varying features such as soil type or accessibility costs for hospitals.

The raster model has evolved to model such continuous features.

A raster image comprises a collection of grid cells rather like a scanned map or picture.

Both the vector and raster models for storing geographic data have unique advantages and disadvantages.

Modern GIS packages are able to handle both models.

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• Primary Focus Geographic Feature Location

(Thing) ( Place )

• Question asked “what do I know about “what phenomenon this geographic feature?” occur at this location?”

• Representation better for precise or better for continuous data discrete kinds of features or change in values along

a gradient

• Accuracy accurate portrayal of feature shape isfeature shape generalized

• Modeling capability requires complicated simple mathematicgeometric algorithms combination of cells

Comparing Vector and Raster Models

Vector Raster

MAP OVERLAYS

Because each cell in a two dimensional array can only hold one number, different geographical attributes must be represented by separate sets of Cartesian arrays, known as ‘overlays’.

The overlay idea for separating data is not restricted to computer cartography, having been used by cartographers for preparing printed maps and by landscape planners. The overlays concept is realized by stacking two dimensional array in raster data structures.

Vector data (the streets) laid on top of raster data (the mountains and valley floor).

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Organizing Spatial Features in Common Themes

Creating data “themes” is basically the process of abstracting or simplifying the real world into different components that can be input into a computer.

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The GIS Data Model: Geographic Integration of Information

• Data are organized by layers, coverages or themes (synonymous concepts), with each theme representing a common feature.• Layers are integrated using explicit location on the earth’s surface, thus geographical location is the organizing principal.

Raster Imagery

LAYERS AND COVERAGES:

  

All data of a particular level All data of a particular level of classification, such as of classification, such as roads, rivers or vegetation roads, rivers or vegetation types are grouped into so types are grouped into so called layers or coverage.called layers or coverage.

In this picture, Customers, In this picture, Customers, buildings and streets have buildings and streets have been divided into different been divided into different layers.layers.

This gives their exact This gives their exact locational information which locational information which proves to be very useful.proves to be very useful.      

                                                                                              

DATA STRUCTURE

These are used to organize the data inside the information system.

The choice of data structure affects both; Data storage volume and processing efficiency.

Types :RelationalHierarchicalNetwork

Relational

Data organized in 2-dimensional table

Row-> Record Column is Attribute

Different tables are related through use of a common identifier called KEY.

Relation extracts the information, which are defined by query.

RELATIONAL

Hierarchical

It stores data in a way that a hierarchy is maintained among the data items.

Each node can be divided into one or more additional node.

Stored data gets more and more detailed as one branches further out on tree

Hierarchical

NETWORK

Similar to hierarchy structure except that a node may have more than one parent.

Each node can be divided into one or more additional nodes.

It is limited since pointers must be updated every time a change is made to database.

NETWORK

APPLICATIONS

The potential of Geoinformatics is huge: The potential of Geoinformatics is huge:

►Agricultural developmentAgricultural development

• Land evaluation analysis• Land evaluation analysis

• Change detection of vegetated areas• Change detection of vegetated areas

• Analysis of deforestation and associated • Analysis of deforestation and associated

environmental hazardsenvironmental hazards

• Monitoring vegetation health• Monitoring vegetation health

• Mapping percentage vegetation cover for the• Mapping percentage vegetation cover for the

management of landmanagement of land 

• Degradation

• Crop acreage and production estimation

• Wasteland mapping

• Soil resources mapping

• Groundwater potential mapping

• Geological and mineral exploration

• Snow-melt run-off forecasting

• Monitoring forest fire

• Monitoring ocean productivity etc.

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SummarySummary►GIS is a tool for storage, manipulation and GIS is a tool for storage, manipulation and

output of spatial dataoutput of spatial data► Remote sensing is a primary source of Remote sensing is a primary source of

data for GISdata for GIS►GIS is a useful tool for processing remotely GIS is a useful tool for processing remotely

sensed datasensed data► To use GIS effectively you must To use GIS effectively you must

understand the characteristics of spatial understand the characteristics of spatial data (e.g. data structures, projections, data (e.g. data structures, projections, implications of math algebra, etc.)implications of math algebra, etc.)

Brief HISTORY

1960's1960'sInitial development in North Initial development in North America and use of ComputersAmerica and use of Computers

1970's1970's Introduction of topology in GIS by Introduction of topology in GIS by stable data structuresstable data structures

1980's 1980's Relational database technology Relational database technology became standard, Researches on became standard, Researches on spatial data structuresspatial data structures

1990's 1990's

Recognition of Geoinformatics as a Recognition of Geoinformatics as a professional activity, professional activity,

Spatial information theory as the Spatial information theory as the theoretical basis for GIS.theoretical basis for GIS.