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Geographic Information Systems – An overview



This chapter intends to present before the readers the basics of Geographical Information System (GIS), Remote Sensing (RS) and Global Positioning System (GPS). We think lot of talk is being made about mapping sciences yet the basics need to be redefined and made simpler so that the benefit of these technologies can move into the grassroots level wherein any person, no matter without technical background can understand theses technologies. If these technologies have to percolate in our day-to-day activities it has to be the common man to appreciate and utilize these innovations. GIS, GPS and RS have a variety of uses right from agriculture, archaeology, environment, geology, health, land information system, military, urban and rural development, transportation, telecommunication, power, water resource, natural and man made disasters, oil and natural gas, banking and insurance, business geographics, mobile mapping to name a few.

Let us understand the basics first
All forms of human activity include and involve a measure of geography. Whether you are a restauranteur looking to open up a fast food centre, a geologist seeking a pot of black gold, a stock broker shopping for new investment opportunities, or a suburbanite on a quest for the nearest video store the problems facing you are the age old questions of geography, where, when and how.

We all possess a certain understanding of our immediate surroundings, i.e. our neighborhoods and communities through a natural sense of place, however as we increase the scale of our vision to a local, national or international scope our knowledge and therefore our ability to relate things decreases significantly.

What is GIS?
GIS is an acronym for:

This term is used because GIS tend to deal primarily with `geographic' or `spatial' or 'graphical' features. These objects can be referenced or related to a specific location in space. The objects may be physical, cultural or economic in nature. Features on a map for instance are pictorial representations of spatial objects in the real world. Symbols, colors and line styles are used to represent the different spatial features on the two-dimensional map.

Computer technology has been able to assist in this mapping process through the development of automated cartography (map making) and computer aided design (CAD). Computer programs can now accomplish in minutes and hours tasks, which previously took days or weeks for cartographers and draughtsman to complete.

This represents the large volumes of data, which are usually handled within a GIS. Every graphical object has their particular set of data, which cannot be represented in full details in the map. So all these data have to be associated with corresponding spatial object so that the map can become intelligent. When these data are associated with respective graphical feature these data get turned to information that is now by click of a mouse on any object its corresponding data get highlighted. All information is data but all data are not information.

This term is used to represent the systems approach taken by GIS, whereby complex environments are broken down into their component parts for ease of understanding and handling but are considered to form an integrated whole. Computer technology has aided and even necessitated this approach so that most information systems are now computer based.

Therefore, Geographic Information System (GIS) is a computer based information system used to digitally represent and analyse the geographic features present on the Earth' surface and the events (non-spatial attributes linked to the geography under study) that taking place on it.

Geographical information systems are not restricted to the conventional view of geography, i.e. that of people and places on the Earth's surface. Hidden geographies lie everywhere and a GIS is the perfect tool to take with you on voyages of discovery. Whether you are exploring the hidden facets of the World Wide Web, the complex geography of a printed circuit, the architecture of a combat aircraft, or want to know where the high tension transmission lines pass or the intricate layout of the testimony in the Starr report, a GIS will help pave the way for the success of the expedition by providing the means of visualizing and exploring these uncharted territories.




Components of GIS

A GIS relies on a computer for storage and processing of data. The size of the computing system will depend on the type and nature of the GIS. A small scale GIS will only need a small personal computer to run on, while a large enterprise wide system with larger computers and a host of client machines to support multiple users.

Fig. 1: Components of GIS

At a core of any GIS system lies the GIS software itself providing the functionality to store, manage, link, query and analyze geographic data. In addition to the core GIS software various other software components can be added to provide access to additional sources of data and forms of functionality.

Data for a GIS comes in two forms geographic or spatial data, and attribute or aspatial data. Spatial data are data that contain an explicit geographic location in the form of a set of coordinates. Attribute data are descriptive sets of data that contain various information relevant to a particular location, e.g. depth, height, sales figures, etc. and can be linked to a particular location by means of an identifier, e.g. address, pin code, etc.

Sources of spatial data include paper maps, charts, and drawings scanned or digitized into the system. Digital files imported from CAD or other graphics systems. Coordinate data recorded using a GPS receiver and data captured from satellite imagery or aerial photography.

GIS systems are designed and developed to aid the data management and decision support processes of an organization. The operation of any organization is based on a set of practices and business logic unique to that organization. While some organizations may use a GIS on an ad-hoc basis with each user formulating their own standards of work and methods of analysis others define their business logic into the GIS to streamline certain aspects of their operations. So the methodology applied is another factor for success of any GIS project.

The system users – those who will use the GIS to solve spatial problems – are most often people who are well trained in GIS, perhaps in a specific application of GIS. System operators are responsible for the day-to-day operations of the system, more often performing tasks that allow the system users to function efficiently. GIS suppliers are responsible for providing software support and updates of the software as new and improved methods are put into the system. The Data supplier could be either private or public. The private company may provide internally generated data or data obtained from public agencies modified to better fit needs expressed by the user community. Public agencies, primarily governmental agencies, provide data for large portions of the country. Application developers are generally trained programmers who will provide user interface to reduce the reliance on specialized GIS professionals to perform common tasks. GIS systems analysts are group of people specialize in the study of systems design.

How is data stored in GIS?

  • A GIS stores a representation of the world in the form of layers connected by a common geographical frame of reference.
  • Each of the features on a layer has a unique identifier which distinguishes it from the rest of the features on the layer and allows you to relate it to relevant information stored in external databases, etc
  • This simple yet powerful mode of abstraction, a GIS allows us to capture only those elements of the world that are of interest to us. Different views and data about the world e.g., streets, soils, pipes, cables, vegetation, etc. can be captured and stored in the GIS over time to accommodate the needs of various different users and to reflect changes in the landscape over time.

Fig. 2: Data Storage in GIS

Data Models
All graphical features on the earth can be represented by only three identities that are line, point and polygon.

  • The layers of data are stored in the GIS using one of two distinctly different data models, known as raster and vector.
  • In raster model, a feature is defined as a set of cells on a grid. All of the cells on the grid are of the same shape and size and each one is identified by a coordinate location and a value which acts as its identifier, features are represented by a cells or groups of cells that share the same identifier. The raster model is particularly useful for working with continuous forms of features such as soil types, vegetation etc.
  • In vector, a feature is represented as a collection of begin and end points used to define a set of points, lines or polygons which describe the shape and size of the feature. The vector model is particularly useful for representing highly discrete data types such as roads, buildings, boundaries and the like.
  • Vector GIS can store corresponding information of complex objects more efficiently.

Fig. 3: Data Models in GIS


What can one do using GIS?
It's been said that better information leads to better decisions, however in order to get that information you need to be able to ask the right questions, and in order to ask the right questions you need the right set of tools.

Almost all of the questions and issues we are faced with have a geographical component to them. Questions such as where, when, how, why, what if all have an obvious or hidden geographical component. Therefore a GIS with its ability to link and display different data sets on the basis of a common geography appears to be the perfect set of tools for supporting a decision making process, but that's not the end of the story. It is a very well known fact that when we finally succeed in answering one question, a hundred new ones suddenly come to mind, remember maps are food for thought. The real power of a GIS lies in its analytical capabilities to provide simple solutions to complex questions to become a better-informed individual capable of making better decisions.

Query and Display
One can start your GIS odyssey using simple queries such as show the states of India in different ranges of literacy rate and he can the see the map (Fig. 4).

Fig. 4: Literacy Map of India

Buffer analysis
This help to answer spatial relationship type of questions like how much area is likely to be submerged in case of any dam brust or how much area can get flooded if the water level of a particular river rises 1m above danger mark. Ex. Show me the villages in my district which have access to a medical facility within 8 km from the village (Fig. 5).

Network Analysis
Network operators provide a way of solving network and transportation related questions. It is helpful in finding the shortest routes, alternative routes, pollution free routes and so on which are very important in case of accidents, disasters etc.


Fig. 5: Medical facility reaching 8 KM radius (Villages Benefited)

Overlay Analysis and Terrain Modeling
Our forester friend has in some ways has a need to know where the trees are, but logging trees will have an impact on the ground and the landscape, depending on the type of soils and the slope of the land different patterns of soils erosion may take place, which will impact the local water supply in different ways. The forester will have to evaluate his decision on which trees to cut down not having any drastic impact on the environment.

Fig. 6: Digital Elevation Model

Overlay analysis and terrain modeling are methods used by GIS to answer these types of questions by allowing us to look for areas of overlap, e.g. areas where you own a strand of trees that grow on a particular type of soil, or view the terrain assessing the effects of erosion given the slope of the land, or the visual impact clear cutting will have on the landscape.

There are virtually no limits to the scope of GIS analysis by combining any of the modes of analysis and query tools provided by a GIS you can derive answers to the most complex questions posed by any activity or field of study.