GIS toolglossary

introduction
definition of GIS
GIS applications
geospatial data
data for GIS applications
digital representation of geospatial data

raster based GIS
vector based GIS

introduction

definition of GIS

Like the field of geography, the term Geographic Information System (GIS) is hard to define. It represents the integration of many subject areas. Accordingly there us no absolutely agreed upon definition of a GIS (deMers, 1997). A broadly accepted definition of GIS is the one provided by the National Centre of Geographic Information and Analysis:

a GIS is a system of hardware, software and procedures to facilitate the management, manipulation, analysis, modelling, representation and display of georeferenced data to solve complex problems regarding planning and management of resources
(NCGIA, 1990)

Geographic information systems have emerged in the last decade as an essential tool for urban and resource planning and management. Their capacity to store, retrieve, analyse, model and map large areas with huge volumes of spatial data has led to an extraordinary proliferation of applications. Geographic information systems are now used for land use planning, utilities management, ecosystems modelling, landscape assessment and planning, transportation and infrastructure planning, market analysis, visual impact analysis, facilities management, tax assessment, real estate analysis and many other applications.

Functions of GIS include:
data entry
data display
data management
information retrieval and analysis

A more comprehensive and easy way to define GIS is the one that looks at the disposition, in layers (Figure 1), of its data sets. "Group of maps of the same portion of the territory, where a given location has the same coordinates in all the maps included in the system". This way, it is possible to analyse its thematic and spatial characteristics to obtain a better knowledge of this zone.


Figure. 1. The concept of layers (ESRI)

 


 

 


geospatial data

Geospatial data has both spatial and thematic components.

Conceptually, geographic data can be broken up in two elements:
observation or entity and attribute or variable.
GIS have to be able to manage both elements.

Spatial component: The observations have two aspects in its localisation: absolute localisation based in a coordinates system and topological relationship referred to other observations. Example: The Department of Geomatics is located at the particular coordinate X,Y, or, The Department is located between Grattan Street and Old Engineering Building. A GIS is able to manage both while computer assisted cartography packages only manage the absolute one.

Thematic component: The variables or attributes can be studied considering the thematic aspect (statistics), the locational aspect (spatial analysis) or both (GIS).

 

data for GIS applications includes:
digitised and scanned data
databases
GPS field sampling of attributes
remote sensing and aerial photography

see the Spatial Data Entry module for more information on this
 


digital representation of geospatial data
The advantages of digital versus analogue data are outlined in the table below:

digital
analogue
easy to update
whole map to be remade
easy and quick transfer
(eg via internet)
slow transfer
(eg via post)
storage space required is relatively small (digital devices)
large storage space required
(e.g. traditional map libraries)
easy to maintain
paper maps disintegrate
over time
easy automated analysis
difficult and innacurate to analyse (e.g. to measure areas and distances)