A Geographic Information System (GIS) is a system that integrates software, hardware and geographic information in order to manipulate, analyze, store and display all kinds of geographic information. In English it is called Geographic Information System (GIS).
These systems are often used in scientific research, resource management, asset management, archaeology, environmental impact assessment, urban planning, cartography, sociology, historical geography, marketing, logistics, etc.
Introduction
A Geographic Information System (GIS) is a system for creating, storing, analyzing, and managing spatial data and associated attributes. In the strictest sense, it is a computer system capable of integrating, storing, editing, analyzing, sharing and displaying geographic reference information. In a more generic sense, GIS is a tool that allows users to create interactive queries (user-created searches), analyze spatial information, and edit data. Geographic Information Science is the science underlying applications and systems, taught as a degree program by several universities.
Geographic information systems technology can be used for scientific research, resource management, asset management, environmental impact assessment, development planning, mapping, and route planning. For example, a GIS could allow emergency planners to easily calculate emergency response times in the event of a natural disaster, or a GIS could be used to find wetlands that need protection from pollution.
development history
35,000 years ago, on the walls of caves near Lascaux, France, Cro-Magnon hunters drew pictures of the animals they hunted. Associated with the animal drawings are track lines and counts that are believed to represent migration routes. Although simplistic compared to modern technologies, these early records mimic the two-element structure of modern geographic information systems, an image associated with attribute information.
Possibly the first use of the geographical method, in 1854 John Snow described an outbreak of cholera in London using dots to represent the location of individual cases. His study of the distribution of cholera led to the source of the disease, a contaminated water pump at the heart of the outbreak. While the basic elements of topology and theme existed earlier in cartography, John Snow’s map was unique in that he used cartographic methods to represent groups of a geographically dependent phenomenon for the first time. In the early 20th century, «photo-lithography» was developed, in which maps were separated into layers. The development of computer hardware fueled by nuclear weapons research would lead to general purpose computer «mapping» applications in the early 1960s. The year 1964 saw the development of the world’s first truly operational GIS in Ottawa, Ontario, by the federal Department of Energy, Mines and Resources. Developed by Roger Tomlinson, it was called «Canadian Geographic Information Systems» (CGIS) and was used to store, analyze and manipulate data collected for the Canadian Land Inventory (CLI), an initiative to determine the ability of land to survive. rural Canada by mapping information on soils, agriculture, recreation, wildlife, waterfowl, forestry, and land use at a scale of 1:250,000. A rank rank factor was also added to allow for analysis.
CGIS was the world’s first «system» and was an improvement over «mapping» applications, providing overlay, measurement, and digitizing/scanning capabilities. It supported a continent-spanning national coordinate system, encoded lines as «arcs» with true topology built in, and stored location and attribute information in separate files. As a result of this, Tomlinson has become the «father of GIS».
CGIS lasted into the 1990s and built Canada’s largest digital database of land resources. It was developed as a central computer-based system to support the planning and management of federal and provincial resources. His forte was the analysis of complex data sets across the continent. CGIS was never commercially available. Its early development and success spurred several commercial mapping applications sold by vendors such as ESRI, MapInfo, Intergraph, and CARIS to successfully incorporate many of the features of CGIS, combining the first-generation approach to separating spatial and attribute information with a second-generation approach to organizing attribute data in database structures. The growth of the industry in the 1980s and 1990s was fueled by the increasing use of GIS on Unix workstations and the personal computer. By the end of the 20th century, the rapid growth of various systems had been consolidated and standardized on relatively few platforms, and users were beginning to export the concept of GIS data visualization over the Internet, requiring data format and data transfer standards. More recently, there is a growing flavor of free and open source GIS packages, such as GRASS GIS and Quantum GIS, which run on a number of operating systems and can be customized to perform specific tasks.
techniques used in GIS
data creation
Modern GIS technologies are based on digital information, for which there are various collection methods. The most common method of data creation is digitization, in which a paper map or survey plan is transferred to a digital medium through the use of a computer-aided drafting (CAD) program and georeferencing capabilities. Many GIS programs facilitate this type of data capture in an integrated environment. Other increasingly available spatial data sources include GPS surveys, remote sensing satellite imagery, and airborne sensors such as LIDAR.
Link information from different sources
If you could relate your state’s rainfall information to aerial photographs of your county, you might be able to find out which wetlands dry up at certain times of the year. A GIS, which can use information from many different sources in many different ways, can help with such analyses. The main requirement for the source data is to know the location of the variables. Location can be noted by x, y, and z coordinates of longitude, latitude, and elevation, or by other geocode systems such as ZIP Codes or highway mile markers. Any variable that can be spatially located can be entered into a GIS. Government agencies and non-governmental organizations are producing various computer databases that can be entered directly into a GIS. Different types of data can be entered into a GIS in the form of a map.
A GIS can also convert existing digital information, which may not yet be in map form, into forms that you can recognize and use. For example, digital satellite imagery generated by remote sensing can be analyzed to produce a map-like layer of digital information on land covers. Another well-developed resource for naming GIS objects is the Getty Thesaurus of Geographic Names (GTGN), which is a structured vocabulary containing over 1,000,000 names and other information about places.
Likewise, census data or hydrological tabular data can be converted into map form, serving as thematic information layers in a GIS.
data representation
GIS data represents real-world objects (roads, land use, elevation) with digital data. Real-world objects can be divided into two abstractions: discrete objects (a house) and continuous fields (rainfall or elevation). There are two broad methods used to store data in a GIS for both abstractions: Raster and Vector.
The raster data type consists of rows and columns of cells where a single value is stored in each cell. In most cases, raster data is images (raster images), but in addition to color, the value recorded for each cell can be a discrete value, such as land use, a continuous value, such as rainfall, or a null value if no data is available. While a raster cell stores a single value, it can be extended by using raster bands to represent RGB (red, green, blue) colors, color maps (a mapping between a theme code and an RGB value), or an extended attribute table. with one row for each unique cell value. The resolution of the raster data set is its cell width in Earth units. For example, in a lidar raster image, each cell can be a pixel that represents an area of 3 meters by 3 meters. Normally the cells represent square areas of the ground, but other shapes can also be used.
The vector data type uses geometries such as points, lines (coordinate series of points), or polygons, also called areas (shapes bounded by lines), to represent objects. Examples include property lines in a housing subdivision represented as polygons and well locations represented as points. The features of vectors can be enforced for spatial integrity by applying topology rules such as «polygons must not overlap». Vector data can also be used to represent continuously varying phenomena. Contour lines and triangulated irregular networks (TINs) are used to represent elevation or other values that change continuously. TINs record values at point locations, which are connected by lines to form an irregular mesh of triangles. The face of the triangles represents the ground surface.
There are advantages and disadvantages to using a raster or vector data model to represent reality. Raster data sets record a value for all points in the covered area which may require more storage space than representing data in a vector format which can store data only where it is needed. Rasterized data also allows easy application of overlay operations, which are more difficult with vector data. Vector data may appear as vector graphics used in traditional maps, while raster data will appear as an image that may have a locked appearance to object boundaries.
Additional non-spatial data can also be stored in addition to the spatial data represented by the coordinates of a vector geometry or the position of a rasterized cell. In vector data, the additional data is attributes of the object. For example, a polygon of…