Geographical Information Systems

From SEA.unu.edu/wiki

(based on Rodriguez-Bachiller, 1995)

GIS are computer-based databases that include spatial references for the different variables stored, so that maps of such variables can be displayed, combined and analysed with relative speed and ease. GIS are a combination of a computerised cartography system (that stores map-data) and a database-management system (that stores attribute-data, an attribute being a characteristic of a map-feature, like land use of an area or slope of a road).

GISs can carry out such functions as:

• calculating areas, and sometimes volumes under a certain altitude (like the water content of a lake)
• calculating straight-line distances and, in some systems, distances along networks;
• identifying viewing areas from a point
• identifying the nearest points to selected features
• using distances to construct buffer-zones around some features, with which to include or exclude parts of other maps (buffering)
• interpolating attribute-values between those recorded for a given set of points
• drawing contour-lines using interpolated values between points
• superimposing maps to produce combined maps (map-overlay) of simple maps or of some of the above.

Example:

Click here for an example of GIS use in Germany: see p.15

... and here for how GIS was used for the Trans-European Network: see pp.25-26

Advantages:

• Relatively easy manipulation of large amounts of data
• Allows location-specific impacts to be clearly visualised.
• Its zoning features and its ability to consider several layers of information at a time can be used in sensitivity mapping
• Long-term cost-savings in map-making

Disadvantages:

• Carries out limited range of analytical tasks: essentially provides data description
• rather than real spatial analysis
• Can be expensive, with high start-up costs
• Limited to impacts that have a direct spatial component.

Further reading:

Rodriguez-Bachiller (2001) in Morris, P. and R. Therivel, eds., Methods of Environmental Impact Assessment, UCL Press, London.