Unit 1.0

INTRODUCTION TO GEOGRAPHIC INFORMATION SYSTEM (GIS)

GIS Technology Overview:

The technology of GIS has developed so fast over the past one decade that it is now accepted as an essential tool for the effective use of geographic information. There are many problems such as soil erosion, deterioration of environment, deforestation, population growth, drought conditions, shortage of drinking water etc. These are complex issues and require integrated responses. One difficulty in organizing such integration e.g. among soil, water, vegetation has been the lack of means to link the data in comparable and manageable sets. In order to overcome these difficulties GIS offers entry of many types of data in a single spatial framework and has capability of collection, compilation, storage, retrieval, analysis, manipulation, display and integration of environmental, economic and social data in a single system.

We are presently positioned at the beginning of twenty first century with the fast growing trends in computer technology information systems and virtual world to obtain data about the physical and cultural worlds, and to use these data to do research to solve practical problems. The current digital and analog electronic devices facilitate the inventory of resources and the rapid execution of arithmetic or logical operations. These information systems are undergoing much improvement and they area able to create, manipulate, store and use spatial data much faster and at rapid rate as compared to conventional method.

The handling of spatial data usually involves processes of data acquisition, storage and maintenance, analysis and output generations. For many years, this has been done using analog data sources, manual processing and the production of paper maps. The introduction of modern technologies has led to an increased use of computers and information technology in all aspects of spatial data handling. The software technology used in this domain is Geographical Information System (GIS).

1.1 Basic Defination:

There is no clear-cut definition for GIS. Different people defined GIS according to capability and purposes for which it is applied. Few of the definitions are: -

a)“A computer assisted system for capture, storage, retrieval, analysis and display of spatial data, within a particular organization” (Clarke, 1986)

b)“A powerful set of tools for collecting, storing, retrieving at will, transforming and displaying spatial data from the real world” (Burrough, 1987)

c)“an information technology which stores, analyzes and display both spatial and non-spatial data” (Parker, 1988)

d)“A decision support system involving the integration of spatial referenced data in a problem solving environment” (Cowen, 1988)

e)A system with advanced geo-modeling capabilities” (Koshkariov, Tikunov and Trofimov, 1989).

The above definitions cover wide range of subjects and activities best refer to geographical information, sometimes it is also termed as Spatial Information System as it deals with located data, for objects positioned in any space, not just geographical, a term for world space. Similarly, the term “aspatial data” is often used as a synonym for “attribute data”. E.g. rainfall, temperature, population data etc.

However GIS can be defined more commonly as: -

“GIS is computerized information storage, processing and retrieval systems that have hardware and software specially designed to cope with geographically referenced data and corresponding attribute information (tables, charts and statistics).”

or

“GIS is an organized collection of computer Hardware, Software, Data and Analyst to effectively capture, store, manipulate, analyze and retrieve all types of spatial and non-spatial information.”

Geo-informatics: the discipline that deals with all aspects of spatial data handling is called geoinformatics. It is defined as: -

“Geoinformatics is the integration of different disciplines dealing with spatial information”

It was originally introduced in Canada, and became very popular in other countries. Laurini and Thomson (1992) describe it as “ the fusion of ideas of from geo-sciences and informatics”.

Frequently Used Terms in GIS:

Spatial Information: information about a particular location called spatial data. E.g land use, soil, slope, drainage, road etc

Non-spatial Information: Description of spatial data in the form of table or statistics. E.g. rainfall, chemical data of soil, temperature data etc.

Attribute or Aspatial data: similar to non-spatial data

Coverage, Theme, Feature, Layers: all are different names for spatial data when different GIS softwares are used.

1.2 Objectives of GIS:

GIS is developed to-

  1. Maximize the efficiency of planning and decision making
  2. Provide efficient means for data distribution and handling
  3. Elimination of redundant data base – minimize duplication
  4. Capacity to integrate information from many sources
  5. Complex analysis / query involving geographic reference data to generate new information

For any application there are five generic questions a GIS can answer:

i)Location: what exist at a particular location

ii)Condition: identify location where certain condition exists

iii)Trends: what has changed since ?

iv)Pattern: what spatial pattern exist ?

v)Modeling: what if ……………..?

1.3 History of Development of GIS:

The GIS history dates back 1960 where computer based GIS have been used. The initial developments originated in North America with the organizations such as US Bureau of Census, The US Geological Survey and Harvard University Laboratory.

Environmental System Research Institute (ESRI) was the first to develop the commercial softwares for GIS applications and till date became the landmark in GIS development activities and making the GIS common and easy for one dealing with spatial data.

A sound and stable data structures to store and analyze map data became dominant in the early 1970’s. This has lead to the introduction of topology into GIS.

Another significant break through occurred with the introduction and spread of personal computers in 1980’s. After that it was possible to have a computer on the desk that was able to execute programs that previously could only be run on mainframe computers.

Relational database technology became the Standard Research on Spatial data structures, indexing method and spatial database made tremendous progress.

The 1990’s can be characterized as a period of the break through of object orientation in system and database design, recognition of geoinformatics as professional activities.

Potentiality of GIS is realized in the recent past and now it has become popular among many users for variety of applications.

1.4Components of GIS

GIS comprises of four components.

  1. The Hardware: used to store, process and display.
  2. The Software: used to control and perform operations.
  3. The Data: on which GIS operations are performed (Spatial, non-spatial)
  4. The Expertise (Live ware): the human element required to drive the system to meet needs.

GIS Hardware

The general hardware components of Geographic Information System are the main computer system or the Central Processing Unit (CPU), the terminal, keyboard and the visual display unit (VDU), digitizer, disk drive, plotter, printer etc. The computer or the CPU is linked to a disk drive storage unit, which provide the space for storing data and programs. The digitizer or other device is used to convert data from maps and documents into digital form and send them to the computer.

A plotter or other kind of output device is used to present the results of data processing, a tape drive is used for storing / retrieving data or programs on magnetic tapes or with other systems. The user interacts with the computer and the peripherals (a general term for digitizer, printers, plotters and other apparatus linked to the computer) via terminals.

Softwares: The GIS softwares to carry out the GIS operations. These are required for driving the hardware. Common interfaces in GIS are menus, graphical icons and commands. Most Common GIS Softwares available in the market are : ESRI products like Arc/Info, Arcview, ArcGIS, Map Info from Map Informatics Inc, Intergraph, Ilwis etc.

Data: includes both spatial and non-spatial data on which GIS operations are performed to derive new information. Spatial data from various sources such as Remote sensing images, Aerial Photographs or Map Data can be integrated with corresponding non-spatial data in GIS.

Live Ware or Analyst: equally important as the computer hardware and software, the brain ware refers to the purpose and objectives, and provides the reason and justification, for using GIS.

1.5 Capabilities of GIS

A GIS is a computer-based system that provides four sets of capabilities to handle georeferenced data.

a)Data inputs

b)Data management (data storage and retrieval)

c)Manipulation and analysis

d)Output.

a) Data Input:

The function of data input to convert data from their existing form into one that can be used by GIS. Georeferenced data are commonly provided as proper maps, table of attributes and associated attribute data, aerial photos and satellite imagery.

Digitization: The process of converting the analog information into digital information is called Digitization. Information on a map can be captured by digitizing each feature. Thus the process of digitization is which converts the spatial features on a map into digital format. Therefore, point, line and area features that compose a map are converted into X & Y co-ordinates, where a single co-ordinate represents a point and a string of co-ordinates represent a line.

Digitization can be done either using digitizing tablet (Head up digitization) or on the screen digitization using mouse through scanning and can be stored either as scanned image or vector coverage.

Digitizing tablet is a device in graphic peripherals, which allows the user to select point from a map, and automatically enters its X, Y co- ordinates in the computer. Digitizing tablet consists of tiny wires both horizontally and vertically inside the board forming a grid. When the tablet is placed on the board, the cross hair on the tablet allows the user to locate visually a point on the map.

Once the point is identified electrical impulse is triggered. Since both tablet and digitizing table is connected to the computer, the exact location of the impulse in relation to the nearest intersection of the electronic grid is known.

This allows the computer to translate the location of the point on the table into the location represented on the map, because the map has been registered on table previously by the user.

Since most systems are interactive the location of the tablet on the table is simultaneously displayed on graphic display screen.

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b) Data Storage and Database Management:

The data storage and management are the functions of database management system of GIS. They are concerned with the way the data is structured, handled, accessed and perceived by the user of the system.

Effective data management includes all related aspect like data security, data integrity, data filling and accessibility and data maintenance abilities.

Data security ensures security against modification of GIS or access of data to unauthorized use.

Data integrity defines the ability of the system to protect data from accidental loss or from contamination by extraneous data. Filling and accessibility provides an authorized user to organize data into categories, directories, study area etc.

Data maintenance provides the authorized user with the ability to update, delete or add data to the GIS database.

Data Processing: Data processing operations are those performed on the data to produce information. It includes removal of errors and updating or matching them to other data. Errors can arise during an encoding and in-putting of spatial and non-spatial data which can be either incomplete or double, in the wrong place at the wrong scale, distorted or linked to the wrong non-spatial data. Besides, data may be over defined and may need to be reduced in volume. Data editing is interactively performed to ensure that all the errors are corrected, updated and properly verified to achieve the required accuracy, which are vital to analysis.

c) Manipulation and Analysis:

Data conversion is only part of the input phase of GIS. What is next is the ability to interprete and to analyze qualitatively and quantitatively the information that has been collected.

Spatial analysis tools are used to model, make predictions and reach conclusion about the problem of interest. Such analysis involves combining data from multiple spatial data categories and performing analysis/statistical operations on the GIS datasets to transform the data into information suitable for a given application.

Typical operation includes overlaying different thematic maps, computing areas, performing proximity searches, buffer zone creation, performing logical operations, scale changing etc.

Other techniques are creation of 3D perspective view using elevation data and generation of slope maps, network analysis, costing etc. Given in brief a few illustrations of some of these techniques.

Overlay
Buffer Generation
Clipping

Proximity Search

Modeling

d) Data Presentation /Output:

Display and conversion operations produce graphic output and reports such as maps and color display drawn on a graphic terminal as well as formulated reports of tabular information, where geographic entities are represented as a series of points, lines and symbols.

Data Integration:

The image processing hardware and software in general provide the most suitable environment for manipulating spatial data in general. In order to achieve more effective information extraction from remotely sensed data, it has been found necessary to combine spatial data acquired from various other sources with additional environmental data sets. One such tool is Geographic Information System (GIS). GIS facilitates integration of data from various sources such as maps, photographs, satellite images, socio-economic data and other tabular statements into a format the allows data to be compared and inter related for extraction of information to make decisions about the real world.

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