Saturday 3 March 2012


A geographic information system is a system designed to capture, store, manipulate, analyze, manage, and present all types of geographically referenced data. The acronym GIS is sometimes used to mean geographical information science or geospatial information studies; these latter terms refer to the academic discipline or career of working with geographic information systems. In the simplest terms, GIS is the merging of cartography, statistical analysis, and database technology.
Therefore, in a general sense, the term describes any information system that integrates, stores, edits, analyzes, shares, and displays geographic information for informing decision making. The term GIS-centric, however, has been specifically defined as the use of the Esri ArcGIS geodatabase as the asset/feature data repository central to computerized maintenance management system (CMMS) as a part of enterprise asset management and analytical software systems. GIS-centric certification criteria has been specifically defined by the National Association of GIS-Centric Solutions (NAGCS). GIS applications are tools that allow users to create interactive queries (user-created searches), analyze spatial information, edit data in maps, and present the results of all these operations. Geographic information science is the science underlying geographic concepts, applications, and systems.




Modern GIS technologies use digital information, for which various digitized data creation methods are used. The most common method of data creation is digitization, where a hard copy map or survey plan is transferred into a digital medium through the use of a computer-aided design (CAD) program, and geo-referencing capabilities. With the wide availability of ortho-rectified imagery (both from satellite and aerial sources), heads-up digitizing is becoming the main avenue through which geographic data is extracted. Heads-up digitizing involves the tracing of geographic data directly on top of the aerial imagery instead of by the traditional method of tracing the geographic form on a separate digitizing tablet (heads-down digitizing).

Relating information from different sources

GIS uses spatio-temporal (space-time) location as the key index variable for all other information. Just as a relational database containing text or numbers can relate many different tables using common key index variables, GIS can relate otherwise unrelated information by using location as the key index variable. The key is the location and/or extent in space-time.
Any variable that can be located spatially, and increasingly also temporally, can be referenced using a GIS. Locations or extents in Earth space–time may be recorded as dates/times of occurrence, and x, y, and z coordinates representing, longitude, latitude, and elevation, respectively. These GIS coordinates may represent other quantified systems of temporo-spatial reference (for example, film frame number, stream gage station, highway mile-marker, surveyor benchmark, building address, street intersection, entrance gate, water depth sounding, POS or CAD drawing origin/units). Units applied to recorded temporal-spatial data can vary widely (even when using exactly the same data, see map projections), but all Earth-based spatial–temporal location and extent references should, ideally, be relatable to one another and ultimately to a "real" physical location or extent in space–time.
Related by accurate spatial information, an incredible variety of real-world and projected past or future data can be analyzed, interpreted and represented to facilitate education and decision making. This key characteristic of GIS has begun to open new avenues of scientific inquiry into behaviors and patterns of previously considered unrelated real-world information.

Data representation

GIS data represents real objects (such as roads, land use, elevation, trees, waterways, etc.) with digital data determining the mix. Real objects can be divided into two abstractions: discrete objects (e.g., a house) and continuous fields (such as rainfall amount, or elevations). Traditionally, there are two broad methods used to store data in a GIS for both kinds of abstractions mapping references: raster images and vector. Points, lines, and polygons are the stuff of mapped location attribute references. A new hybrid method of storing data is that of identifying point clouds, which combine three-dimensional points with RGB information at each point, returning a "3D color image". GIS Thematic maps then are becoming more and more realistically visually descriptive of what they set out to show or determine.

Data capture

Data capture—entering information into the system—consumes much of the time of GIS practitioners. There are a variety of methods used to enter data into a GIS where it is stored in a digital format.
Existing data printed on paper or PET film maps can be digitized or scanned to produce digital data. A digitizer produces vector data as an operator traces points, lines, and polygon boundaries from a map. Scanning a map results in raster data that could be further processed to produce vector data.
Survey data can be directly entered into a GIS from digital data collection systems on survey instruments using a technique called coordinate geometry (COGO). Positions from a global navigation satellite system (GNSS) like Global Positioning System (GPS), another survey tool, can also be collected and then imported into a GIS. A current trend in data collection gives users the ability to utilize field computers with the ability to edit live data using wireless connections or disconnected editing sessions. This has been enhanced by the availability of low cost mapping grade GPS units with decimeter accuracy in real time. This eliminates the need to post process, import, and update the data in the office after fieldwork has been collected. This includes the ability to incorporate positions collected using a laser rangefinder. New technologies also allow users to create maps as well as analysis directly in the field, making projects more efficient and mapping more accurate.
Remotely sensed data also plays an important role in data collection and consist of sensors attached to a platform. Sensors include cameras, digital scanners and LIDAR, while platforms usually consist of aircraft and satellites. Recently with the development of Miniature UAVs, aerial data collection is becoming possible at much lower costs, and on a more frequent basis. For example, the Aeryon Scout was used to map a 50 acre area with a Ground sample distance of 1 inch (2.54 cm) in only 12 minutes.
The majority of digital data currently comes from photo interpretation of aerial photographs. Soft-copy workstations are used to digitize features directly from stereo pairs of digital photographs. These systems allow data to be captured in two and three dimensions, with elevations measured directly from a stereo pair using principles of photogrammetry. Currently, analog aerial photos are scanned before being entered into a soft-copy system, but as high quality digital cameras become cheaper this step will be skipped.
Satellite remote sensing provides another important source of spatial data. Here satellites use different sensor packages to passively measure the reflectance from parts of the electromagnetic spectrum or radio waves that were sent out from an active sensor such as radar. Remote sensing collects raster data that can be further processed using different bands to identify objects and classes of interest, such as land cover.
When data is captured, the user should consider if the data should be captured with either a relative accuracy or absolute accuracy, since this could not only influence how information will be interpreted but also the cost of data capture.
In addition to collecting and entering spatial data, attribute data is also entered into a GIS. For vector data, this includes additional information about the objects represented in the system.
After entering data into a GIS, the data usually requires editing, to remove errors, or further processing. For vector data it must be made "topologically correct" before it can be used for some advanced analysis. For example, in a road network, lines must connect with nodes at an intersection. Errors such as undershoots and overshoots must also be removed. For scanned maps, blemishes on the source map may need to be removed from the resulting raster. For example, a fleck of dirt might connect two lines that should not be connected.

GIS developments

Many disciplines can benefit from GIS technology. An active GIS market has resulted in lower costs and continual improvements in the hardware and software components of GIS. These developments will, in turn, result in a much wider use of the technology[original research?] throughout science, government, business, and industry, with applications including real estate, public health, crime mapping, national defense, sustainable development, natural resources, landscape architecture, archaeology, regional and community planning, transportation and logistics. GIS is also diverging into location-based services (LBS). LBS allows GPS enabled mobile devices[28] to display their location in relation to fixed assets (nearest restaurant, gas station, fire hydrant), mobile assets (friends, children, police car) or to relay their position back to a central server for display or other processing. These services continue to develop with the increased integration of GPS functionality with increasingly powerful mobile electronics (cell phones, PDAs, laptops).

OGC standards (Open Geospatial Consortium)

The Open Geospatial Consortium (OGC) is an international industry consortium of 384 companies, government agencies, universities and individuals participating in a consensus process to develop publicly available geoprocessing specifications. Open interfaces and protocols defined by OpenGIS Specifications support interoperable solutions that "geo-enable" the Web, wireless and location-based services, and mainstream IT, and empower technology developers to make complex spatial information and services accessible and useful with all kinds of applications. Open Geospatial Consortium (OGC) protocols include Web Map Service (WMS) and Web Feature Service (WFS).
GIS products are broken down by the OGC into two categories, based on how completely and accurately the software follows the OGC specifications.
Compliant Products are software products that comply to OGC's OpenGIS Specifications. When a product has been tested and certified as compliant through the OGC Testing Program, the product is automatically registered as "compliant" on this site.
Implementing Products are software products that implement OpenGIS Specifications but have not yet passed a compliance test. Compliance tests are not available for all specifications. Developers can register their products as implementing draft or approved specifications, though OGC reserves the right to review and verify each entry.

Web mapping

In recent years there has been an explosion of mapping applications on the web such as Google Maps and Bing Maps. These websites give the public access to huge amounts of geographic data.
Some of them, like Google Maps and OpenLayers, expose an API that enable users to create custom applications. These toolkits commonly offer street maps, aerial/satellite imagery, geocoding, searches, and routing functionality.
Other applications for publishing geographic information on the web include Cadcorp's GeognoSIS, ESRI's ArcIMS Server, Google Earth, Google Fusion Tables, and the open source alternatives of MapServer, Mapnik, and GeoServer.

Global change, climate history program and prediction of its impact

Maps have traditionally been used to explore the Earth and to exploit its resources. GIS technology, as an expansion of cartographic science, has enhanced the efficiency and analytic power of traditional mapping. Now, as the scientific community recognizes the environmental consequences of anthropogenic activities influencing climate change, GIS technology is becoming an essential tool to understand the impacts of this change over time. GIS enables the combination of various sources of data with existing maps and up-to-date information from earth observation satellites along with the outputs of climate change models. This can help in understanding the effects of climate change on complex natural systems. One of the classic examples of this is the study of Arctic Ice Melting.
The outputs from a GIS in the form of maps combined with satellite imagery allow researchers to view their subjects in ways that literally never have been seen before. The images are also invaluable for conveying the effects of climate change to non-scientists.

Benefits due to increased efficiency are considered the easiest to quantify (Prisley 1987) and can be achieved by enhancement of productivity (Antenucci 1991). An enhanced productivity can be achieved during GIS implementation in different ways:
  • The staff has accurate and up to date information available.
  • Tasks can be performed accelerated by sharing and processing of graphics and attribute data in combination with sketches and rasterized informations; tedious search of information in different departments and locations can be avoided.
  • Interdepartmental cooperation for optimum planning, implementation, and operation of municipal services becomes feasible.
  • The overhead for the production, updating, and reproduction of maps including the analogue base map is reduced. The staff resources required for updating the maps are reduced. Often, however, savings are re-allocated due to introduction of additional information products and of additional evaluation processes (Knepper 1991, Smith 1992).
  • Automatic data transfer of tachymetric data acquisition allows easy data input.
  • Manually drawn maps are deteriorated due to use and age and must be redrawn. Using GIS technology it is possible to redraw maps if required.
  • Using mobile computer it can be more cost effective to provide information digitalle than it is to provide paper copies of required maps (Webb 1994).
Operational Benefits
Operational benefits correspond with capacity enhancements by higher human or technical ressources. Aspects of operational benefits are to a great extent independent of the selected system. Possible operational benefits are:
• Enhancements to data quality (completeness, positional and attribute accuracy); higher degree of actuality;. The data quality is enhanced by applying system internal checks to data conversion and update (topological consistency, correctness and completeness of attributes).
User friendliness: Accelerated provision of information; generation of different thematic maps, flexible selection of area and scale; faster compilation of technical reports, statistical and logical evaluation based on data selection and combination of descriptive data, tabular data and spatial data; descriptive data are visualized on the bases of spatial phenomena; information in the right form, in a timely fashion;
• Different departments will access and use the same geographic database;
Unification of graphical presentation corresponding to official cartographic standards;
• High level of public service;
Integration of technical calculations for project engineering and operation; net simulation and tracing, net inventory: Evaluation of age and damages supports scheduling maintenance and repairs for technical infrastructure as road and sewerage network. Maintenance requirements can be prioritized, predictive methodologies can be applied for multi-year repair or investment plans (Dahlgren 1994). The availability of an engineering information base will allow engineers to conduct strategic planning studies by identifying the under-utilized parts of a network (Eaton 1994).

Basic research into the relationship between GIS and society is of significance to the national research agenda for a multitude of reasons. GIS technology is now found in nearly all Federal and state government agencies, educational institutions and large private firms, and is now rapidly being adopted by local governments, environmental organizations, neighborhood organizations, and small firms. Increasingly, spatial data are being shared among these organizations. The technology has metamorphosed beyond a simple mapping tool to a methodology that is used for urban planning, environmental monitoring/analysis, marketing, transportation, management, and analyzing complex spatial problems. While there are many ways in which human activities can be carried out more effectively and democratically through the application of GIS, it is equally clear that GIS can create unintended consequences which reinforce existing social and spatial inequalities and intrude into private lives. NSF and the NAS have become concerned in general with the ethical, legal and social dimensions of information technologies, and there are particular dimensions of this associated with the visual power and locational precision of GIS. In order to limit the undesirable consequences of GIS, to create new geographic information technologies of relevance and use to all members of society, and to remain critically aware of the unintended consequences of access to geographic information, the study GIS and society is essential.

1991: Geographic Information Systems: a guide to the technology. Van Nostrand Reinhold, New York, 301 S., ISBN 0-442-00756-6
Behr, F.-J., 1994: Erhebung von Nutzenaspekten bei der Einf├╝hrung
geographischer Informationssysteme. Geo-Informations-Systeme, Vol 7, No. 2, 1-8
Born, J., 1992: Ist die Einf├╝hrung von GIS durch Kosten-/Nutzenanalyse
entscheidbar? in: Proceedings AM/FM/GIS European Conference VIII, Montreux, 49 - 56
Clarke, A.L., 1991: GIS Specification, Evaluation, and Implementation. in:
Maguire, D.J., Goodchild, M.F., Rhind, D.W. (Eds.): Geographical Information Systems: principles and applications. Longman, London, S. 477-488
Clarke, K. C., 1986. Advances in geographic information systems,
computers, environment and urban systems, Vol. 10, pp. 175–184.
Chang, K. T. (2008). Introduction to Geographical Information Systems. New York: McGraw Hill. p. 184. 


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