Sunday, September 13, 2015

Birth and History of GIS

The primary force behind the development of GIS was thematic cartography. visualization and generation of application of application-specific maps. Traditional cartographic processes were human intensive, inflexible and error-prone. With the arrival of new technologies like surveying using GPS, aerial photography and photogrammetric interpretations of remotely sensed images the manual cartographic process  was replaced by digital cartographic process resulting in reduced dependence on human skill and eliminating errors in the process. The basic concepts of digital cartography can be traced to the work done by the Land Inventory Branch of the Canadian Government and the HARVARD lABORATORY FOR COMPUTER GRAPHICS AND SPATIAL ANALYSIS. Commercial GIS like ARC/INFO and Geomedia suit of solutions considered to be the first generation GIS were launched by Environmental Systems Research Institute (ESRI) and Intergraph respectively. Other popular GIS softwares are Geographic Resource Analysis Support System (GRASS), Quantum Geographic Information System (QGIS), System for Automated Geoscientific Analysis (SAGA) and many more available in the public domain for free.

GIS helps answer questions about:
-Locations
-Patterns
-Trends and
-Conditions

Before the advent of GIS, the analysis of the large volumes of spatial data coupled with time constraints and limited techniques made this process very difficult or impossible.  GIS techniques help in quick remodelling for modifications in the geographic context. The end product of a GIS is map used for public appraisal and feedback.  One of the most convenient aspects of a GIS is that it permits repetition of the analysis of a problem for a modified set of conditions on the same base map to evaluate options in a detailed and scientific manner.

GIS can also be used as a tool for policy formulation.
GIS can be used for environmental management problems and is currently being used by environmental managers all over the world.

GIS is a computer system covering three main components:
-Hardware
-Software module and Appropriate procedures
- Proper organizational context (Trained personnel)

GIS uses spatially referenced or geographical data. It performs management and analysis tasks on these data. Output of GIS is mainly in the form of maps, graphs, text and summary statistics. GIS is used to add value to spatial data.

GIS software has been designed to handle spatial data. Spatial data are characterised by
-information about position
-connection with other features and
-details about non spatial characteristics

The method of representing geographic space occupied by spatial data as a series of thematic layers is known as LAYER-BASED APPROACH.

Features in the real world are expressed in the computer as discrete objects. This method is known as OBJECT-ORIENTED APPROACH.

All geographic features are classified into THREE TYPES for entry into a GIS. They are:
-POINTS
-LINES &
-POLYGONS or AREAS

Data input and updating are the most important, expensive, complex and time-consuming part of a GIS project.

The ability of GIS to transform spatial data and perform spatial analysis distinguishes it from other types of information systems.

Aronoff (1989) classified GIS analysis procedures into three types:
-Storage and retrieval
-Constrained queries and
-Modelling procedures (what-if scenarios)

Data layers in a GIS contain data of ONLY ONE ENTITY TYPE. (Point or line or area data)

GIS has become an accepted tool for the management and analysis of spatial data.

All GIS are computer representations of some aspect of the real world.

The simplified view of the real world adopted by GIS is often termed as a model.

Data is simply a collection of alphanumeric characters with no meaning. Data to which a context is added becomes meaningful. Hence, Information is data to which meaning and context are added(Hanold, 1972). Data can be PRIMARY or SECONDARY. This data has three dimensions:
-Temporal (WHEN the data was collected)
-Thematic (describing the CHARACTER) and
-Spatial (WHERE the object or phenomena occurs)

In GIS, the thematic data are generally referred to as NON-SPATIAL or ATTRIBUTE DATA

Distinction between thematic and topographic maps is that thematic maps display data related to a particular theme such as soil, geology, geomorphology, landuse, population, natural resources, etc while topographic maps contain a diverse set of data on different themes. For example: land use, relief and cultural features may appear together on the same topographic map. Unwin (1981) argues that "a topographic map is simply a composite of different kinds of maps".

Topology is simply the geometric relationships of objects.

The method chosen to represent a spatial feature depends on the scale of the map. The relationship between scale and detail is called SCALE RELATED GENERALIZATION.