Geographic Information Systems: An Introduction, 3rd Edition

3.3 Data Model

A real-world model facilitates the study of a selected area of application by reducing the number of complexities considered. Those outside the selected area are considered insignificant. However, if a real-world model is to be of any use, it must be realized in a database. A data model makes that possible.

Unlike humans, computers cannot “learn” the essentials of manholes, property lines, lakes, or other types of objects. What they can do is to manipulate geometric objects such as points, lines, and areas, which are used in data models. The carriers of information in data models are known as objects (Figure 3.3) or features.^* These correspond to entities in real-world models and are therefore regarded as abstractions of real-world phenomena.

Figure 3.2

Modeling process. The transformation of the real world into GIS products is achieved by means of simplification and models in the form of maps and reports.

Figure 3.3

In a data model, objects are categorized as object classifications, geometric elements (point, line, area), attributes, relations between the entities, and quality definitions of these descriptive elements.

Objects are characterized by:

• Type
• Attributes
• Geometry
• Relations
• Quality

Real-world models and entities cannot be realized directly in databases, ...