Geographic Information System- An overview


Components of GIS

Hardware
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

Software
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
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.

Methods
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.

People
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


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