Geographic Information Systems: An Introduction, 3rd Edition

3.1 The Real World

In many ways GIS presents a simplified view of the real world. Since the processes involved are seldom straightforward because realities are irregular and constantly changing, perception of the real world depends on the observer. For example, a surveyor might see a road as two edges to be surveyed, the roadwork authority might regard it as an asphalt surface to be maintained, and the driver will see it as a highway. Moreover, the real world may be described in terms of countless phenomena, from basic subatomic particles up to the dimensions of oceans and continents. The complexity of the real world, as well as the broad spectrum of its interpretations, suggests that GIS system designs will vary according to the capabilities and preferences of their creators. This human factor can introduce an element of constraint, as data compiled for a particular application may be less useful elsewhere.

The systematic structuring of the data determines its ultimate utility and, consequently, the success of the relevant GIS application. This aspect is also characteristic of the data available in traditional maps and registers. The real world can be described only in terms of models that delineate the concepts and procedures needed to translate real-world observations into data that are meaningful in GIS. The process of interpreting reality by using both a real-world and a data model is called data modeling. As illustrated in Figures 3.1 and 3.2, the elements involved are: