A Geographic Information system or a GIS is a tool to capture, store and managing data which are spatially related to Earth. In close terms, the system is related to managing, integrating, storing and analyzing geographically referenced information. Geographic Information system is used in the process of scientific research, natural resource management, impact of pollution on environment, land use and planning, company sales and marketing and criminology. For example, Geographic Information system is often used energy planners who need to calculate the emergency response times during an emergency like a natural disaster.
Also, Geographic Information system is used to find the areas that are affected by pollution – wet lands or used by companies to take advantage of an untapped economy or an unreserved market. HISTORY OF GIS The first use of a Geographic Information system is that recorded in 1854, by Sir John Snow. In the event of Cholera outbreak in London, he used a map which directed signs towards the individual cases of cholera in the city. This study which helped the administration to reach to the source of the outbreak, which was an infected water pump. After knowing the root cause of the outbreak, immediate steps were taken by the administration.
This strategy of John Snow to collect all the information about the cholera cases in the city on a geographical map of the city and then to analyze the information at hand, thereby reaching at some conclusions that were helpful in fighting with the outbreak is the true essence of a Geographic Information system. Fig 1: Map showing clusters of Cholera cases in London by John Snow In the year 1962, the true face of Geographic Information system came into existence with the Federal Department of Rural development in Canada. The first Geographic Information system was developed by Dr.
Roger Tomlinson, and was to help the Land inventory department to gather and analyze information related to the land use and capability, soil structure and forest area in Ontario. This system possessed some enhanced features like – mapping, overlaying, measurement, scaling and scanning. It also had a co-ordinate system that could inter relate every other part of the continent and could scale huge areas into very small ones. The use of overlays in extending the method of spatial analysis of geographical data was also included in this first Geographic Information system.
However, this Geographic Information system was never brought out into the market for commercialization purposes. The first commercial Geographic Information system was developed during the late 1980’s by the M&S Computing research Institute and this commercial Geographic Information system had a successful combination of the first Geographic Information system developed in 1962 by Sir John Snow. It had the technique of spatial attribution, and organizing of data with the help of database structures.
With the onset of the 20th century, there was a fast growth in the development of commercial Geographic Information systems to transport, gather and analyze data in all commercial fields. Recently, there has been an increase in the number of free open source commercial Geographic Information systems which can be used in accordance with a number of operating systems and can also be customized top match up some specific tasks. DATA CREATION IN GEOGRAPHIC INFORMATION SYSTEM The Geographic Information Systems that exist today make use of the information that is present in the digital form.
The methods of data creation for a Geographic Information system are many and the most commonly accepted method for data creation of digital data is digitization. In this method, Computer aided design method is used to transfer the data present on a hard copy, into a digital form, and geo-referencing capabilities. Another popular form of extracting geographical data into digital form is by ortho-rectified imagery, in which head up digitizing is the main way through which tracing of geographical data is done directly rather than traditionally tracing the geographical data on a different digitizing tablet.
LINKING INFORMATION FROM VARIOUS ORIGINS With the help of Geographic Information Systems, a myriad of information gathering is possible. Suppose for example, if the rainfall data about a particular state and its aerial snaps or the area are gathered, then it relatively easier to predict the area which dries up during summer. A Geographic Information Systems can make use of various forms of information by linking them together and analyzing the whole bunch together. The elementary requirement for knowing the exact source of data is the knowledge of variables.
The location of a certain area is denoted by x,y,z coordinates, where x corresponds to Longitude, y corresponds to latitude and z corresponds to elevation. These values may vary according to the needs and types of data required. A Geographic Information System is capable of changing any form of digital data into usable form that is recognized by the system and is used. For instance, the satellite images that are generated with the help of remote sensing satellites are processed by a Geographic Information System to corresponding map like information which can be easily read by the Geographic Information System.
Similarly, the hydrologic tabular data in the tabular form can be converted into a data map, which is used as layers of information in a Geographic Information System. DATA REPRESENTATION The Geographic Information System offers the presentation of real time objects like land, roads, height etc, in the digital form. However, the real time data is further divided into two types: discrete and continuous data. Discrete data includes data like a building, area of land, while continuous data represents level of rain, height of a particular area, or elevation.
There are two main methods of storing data in a Geographic Information System for both discrete and continuous forms. 1. Raster method – this form of data is stored in the form of cell rows and cell columns, where a single value data is stored in each cell. Since raster is used to store a single data, in each cell, continuous forms of data an extended table of more than one row or column is used. 2. Vector Method – in a Geographic Information System, it is often needed to express data in the form of vectors.
In order to store data which possesses some sort of direction, use of polygons is made in the Geographic Information Systems. These polygons or geometrical shapes are also called as Shape files. Zero dimensional points, one dimensional lines, two dimensional polygons are some examples of shape files used in Geographic Information Systems. Points are used to denote real time objects like location of a school, building, home, well etc. lines are used to denote roads, railway lines, rivers etc. polygons are used to point to an area of land, city boundaries, water bodies etc.
Each of these geometric shapes / geometries are associated with single rows in the database of the Geographic Information System, and this describes their characteristics completely. For example, consider a Geographic Information System data base that gives information about the various lakes in a particular area, their depth, and quality of water, color of water and the level of pollutants that are mixed with water. These sets of information can be each used separately to make a map to describe that particular data set.
Also, the Geographic Information Systems can be used to identify and locate the wells that are present in the area, in particular that are within the one mile area of the lake. The wells are identified as point geometry and the lakes as polygon geometry in the Geographic Information System data map sets. Vector characteristics in a Geographic Information System data set can also be altered to maintain the spatial characteristic or integrity of a particular data / location, with the application of certain topology rules. A simple basic rule used in Geographic Information Systems is that the polygons must never overlap each other.
The vector data sets can be appropriately used to represent the continuous data sets or continuously varying information. The contour lines and triangulated discontinuous areas and networks are used to characterize the elevation / height above sea level and other examples of continuous values. The triangulated discontinuous areas record the values of a point location which are in the form of a mesh formed with the help of lines connected from each other signifying other areas and point locations. For example, the face of a mesh in the form of a triangle is used to represent the terrain surface in Geographic Information Systems.
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