Further description:-  Geographical information systems 

Glossary Entry
a computer system to assemble, store, manipulate, and display geographically-referenced information, 
i.e. data identified according to their locations. Geographic information systems (GIS) technology
can be used for scientific investigations, resource management and development planning.
Geographic Information Systems (GIS)

Geographic Information Systems (GIS)

 

1. Summary

 

A GIS is a computer system capable of capturing, storing, analyzing, and displaying geographically referenced information; that is, data identified according to location. A GIS can be used in several different ways. For example, it might allow emergency planners to easily calculate emergency response times in the event of a natural disaster, or a GIS might be used to find wetlands that need protection from pollution. In our use of GIS we should recognize that the object of study usually has a geographic dimension and a temporal dimension, which means that the object (e.g. a lake) has different characteristics for different locations and different characteristics for different moments in time.

 

2. Working Stages

 

Three fundamental stages of working with geographic data can be distinguished:

 

  • Data preparation and entry: The early stage in which data about the study phenomenon is collected and prepared to be entered into the system.
  • Data analysis: The middle stage in which collected data is carefully reviewed, and for instance, attempts are made to discover patterns.
  • Data presentation: The final stage in which the results of earlier analysis are presented in an appropriate way.

 

3. Data Structures

 

Two main data structures can be distinguished in a GIS:

  • Raster data (a regularly spaced set of cells with associated (field) values)
  • Vector data (structures which are represented by points, lines, polygons or TINS (triangular irregular networks))

A GIS must be able to convert data from one structure to another (e.g. raster to vector conversion).

 

4. Data analysis

 

A main advantage of GIS is that different types of data can be combined to obtain new information, e.g. information concerning the groundwater and soil contamination can be combined with hydrologic and land use information to generate risk assessment maps.

If the data is not available in digital form it can be digitised using various techniques. coordinates from Global Positioning Systems (GPS) can also be uploaded into a GIS. A GIS can depict two- and three-dimensional characteristics of the Earth's surface, subsurface, and atmosphere from points where samples have been collected, e.g. two- and three-dimensional contour maps created from pH measurements can be analyzed together with any other map in a GIS covering the area (figure 1).

 

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Figure 1: Contour map made of soil pH values

 

Other successful examples of the application of GIS are colour-shaded relief maps of landings sites for Mars Exploration Rovers (figure 2)

 

Figure 2: Colour shaded relief maps

 

A key to a successful GIS application is the access to the right source of data. Whereas for some regions data can be available for free, for many projects data  has to be bought or generated.

 

5. Data Resources

 

Some useful links where data is available:

 

  • ESRI Data Resources

http://www.esri.com/data/index.html

 

·        GIS Data depot

http://data.geocomm.com/

 

·        Stanford University Information Resources

http://www-sul.stanford.edu/depts/gis/web.html

 

6. GIS Products

 

A wide variety of GIS products for data analysis is available. The GIS products can be divided into freeware and commercial products. A comprehensive list of the available GIS products can be obtained from the Geotechnical and Geo-Environmental Software Directory:

 

http://www.ggsd.com

 

7. Weblinks and guidelines

 

Online GIS dictionary:

http://www.geo.ed.ac.uk/agidict/welcome.html

 

Guidelines for Best Practice in User Interface for GIS:

http://www.gisig.it/best-gis/Guides/main.htm

 

Journal of Geographic Information and Decision Analysis (online Journal):

 

http://www.arts.monash.edu.au/ges/research/Gis/public/e_journal.html

 

Applied GIS (online Journal):

 

http://www.arts.monash.edu.au/ges/research/Gis/public/e_journal.html

 

ESRI Mapmuseum

http://www.esri.com/mapmuseum/

 

8. Literature

 

De By, R.A (2001): Principles of Geographic Information Systems. ITC, Educational Textbook Series 1, 2ed.

 

Worboys, M., Duckham, M (2004): GIS: A Computing Perspective. CRC Press (2 ed.)

 

Van Sickle, J. (2004): Basic GIS Coordinates. CRC Press

 

Authors
Stefan Gödeke
Universität Tübingen, Germany

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