OVERVIEW OF GIS INTRODUCTION:The resource managers, planners and decision-makersdepend on the information related to an area or location for analyzing and implementing developmental plan.Conventional data storage and management has failed to satisfy their needs. With the advent of computers technology the database management in term of where, what has been classed through geographical information system (GIS
What is a Map ? Maps are the main source of data for GIS. What is a map? A map is representation of the spherical surface ofthe earth on the plain sheet of earth. In practice we normally think of two types: 1. Topographic maps 2. Thematic maps
Topogrpahic MapA reference tool, showing the outlines of selected natural and man-made features of the Earth. It often acts as a frame to other information
Thematic maps:A tool to communicate, geographic concept such as the distribution of population densities, climate, soils, landmark etc. Thematic maps are of two types Chloropleth b) IsoPleth
Types of Maps: A Chloropleth map uses reporting zones as censustracts to show data such as average incomes or soil geology etc. An IsoPleth maps shows an imaginary surface bymeans of lines joining points of equal value "Isolates (eg. Controls on a topographic map)
Characterstics of Maps: The general Characteristics of maps are-Maps are often stylized, generalized required careful interpretation -Usually out of date -Show only static situation -Often highly elegant/artistic
What is GIS? GIS stands for geographic information system. GIS has been variously defined as - - "A spatial data handing system"(Marble etal.1980)A computer assisted system for the capture, storage, retrieval, analysis and display of spatial data with in a particular organization (Clark, 1986) A set of tools for collection, storing retrieving at will , transforming and displaying data from the real world for a particular set of purpose (Borough, 1986) continued…..
What is GIS? - 2 An organized collection of hardware, software, geographic data, and personnel designed to efficiently capture, store, update, analyze anddisplay all forms of geographical referenced information(ESRI) or simply Acomputer system capable of holding and using data describing place on the earths surface the last definition needs little elaboration which highlights the components of a GIS are :- Computer hardware Software Spatial data and their attributed and Trained personnel
Uses Of GIS GIS does not function by itself and it must be emphasized that a group of well-trained persons skilledin the technology are crucial components are termed as "Humanware". GIS can be used as a decision support tools in solving increasingly complex urban andenvironmental problems. Forestry and wild Life Tracking. Waste Land Developments, Agriculture and Ground Water Resource water resource Management. Urban application include utilities management, site suitability analysis and demographic studies
What a GIS is not A GIS is not simply a computer for making maps, although it can create maps on different scales and in different projections. A GIS is an analytical tool. The major advantage of a GIS is that it allows one to identify the spatialrelationship between maps features and the non-spatial data.
GIS is a spatial database GIS is a spatial database that answers these: Application (In a typical Agriculture applications) Locations, what is at……? (what crop exits at particular location) Conditions: where is it…..?(which locations satisfy certain conditions) the crop is associated with what soil type or what is the rainfall and so on Trends using temporal data ? Trends can be seen in two points of time (whether a particular crop increases or decreases. Soils have been degraded/eroded or not? etc.) Pattern: what spatial pattern existsThe display of crop zone cover superimposed on village, markets, road networks, as shown a definite pattern
GIS- ModelsModels: "what if" (The GIS analyst can get answerto some assumptions and presumptions like whatwill happen to crop cover (rice/wheat) production ifpopulation is doubled or agriculture area reducedby certain percentage and water holding capacity reduces.
Types of GIS GIS package acts on two types of data models. These are Raster Data Model Vector data ModelBased on the data model, GIS are called as Raster based GIS and vector based GIS
Raster Data ModelThe Raster model divides the entire study area into a regular grid of cells in specific sequence the conventional sequence is row from the top left corner each cell contain a single value it is space filling since every location in the study area correspondents to a cell in the Raster one set of cells and associated values is a layer and there may be many layers in a database, eg soil type, elevation, land cover, etc
Vector Data Model The vector model reduces the entire study area into three geographical identities - the point, the line and the areaevery geographical phenomenon can in principle be represented by a point, line or area plus a label saying "what it is". The label could be the actual be the names, or they could be numbers that cross- reference with a legend, or they could be a special symbola map is a set of points, lines and area that are defined both by theirlocation in space with reference to a coordinate system and by their non spatial attributes vector objects do not necessarily fill space
GIS softwareBased on these two data models there are different GISsoftware packages available in the market. Among these ERDAS, IDRISI, SPANS ILWIS, MAP INFO and ARC/INFO etc are the most popular ones, amongst these ERDAS, IDRISI, ILWIS AND SPAN are Raster based and Map info, ISRGIS and ARC/INFO are vector based GIS software
GIS compared to maps-1 Data StoresSpatial data stored in digital format in a GIS allows for rapid access for traditional as well as innovative purposesMaps can be designed to be easy to convert to digital from e.g. by theuse of different colors which have district signatures when scanned by electronic searching
GIS compared to maps- 2 Data IndexesThis function can be performed much better by a good GIS due to theability to provide multiple and efficient cross-referencing and searching
GIS compared to maps- 3 Data Analysis Tool GIS is a powerful tool for map analysisTraditional impediments to the accurate and rapid measurement of area or to map overly no longer exists Many new techniques in spatial analysis are becoming available
GIS compared to maps- 4 Data Display ToolsElectronic display offers significant advantage over the paper mapAbility to browse across an area without interruption by map sheet boundaries Ability to zoom and change scale freely Display in "3 dimensions" with "real time" rotation of view anglePotential for continuo scales of intensity and the use of color and shading independent of the constraints of the printing process, ability to change as required for interpretation.
Data Input Data input is a process of converting analog data (map features) into adigital form to develop a spatial database for further analysis required fordifferent applications. Data input is carried out through the process called Digitization.Input data to the GIS can come from several source such as digitized maps from the output of digitizing table; Scanned maps from a scanner; ASCII files containing point data with associated coordinated from GPS(Global Positioning Systems) Surveys; text data from published sources such as Census departments; Thematic maps from Satellite imagery etc.
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