Geographical information systems
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.
Three fundamental stages of working with geographic data can be distinguished:
3. Data Structures
Two main data structures can be distinguished in a GIS:
A GIS must be able to convert data from one structure to another (e.g. raster to vector conversion).
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).
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.
Some useful links where data is available:
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:
Online GIS dictionary:
Guidelines for Best Practice in User Interface for GIS:
Journal of Geographic Information and Decision Analysis (online Journal):
Applied GIS (online Journal):
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