Introducing Geographic Information Systems with ArcGIS: A Workbook Approach to Learning GIS, 3rd Edition

Objects—First Acquaintance

A more profound difference between the depiction of features in the coverage data model and that of the geodatabase is that features are not just geometric entities with attributes, but objects, in the computer science sense of the word.

The study of electricity and magnetism is customarily divided into two general areas: fields and circuits. The term fields refers to the characteristics of the invisible forces that are caused by magnetic material or by current flowing in a wire. The term circuits refers to the study of electricity where electrons are confined to wires and other elements. You might think of a loose analogy between fields and areal features, on one hand, and circuits and linear (network) features, on the other. In networks, entities such as trucks and gas molecules are confined within physical structures, as the electrons are confined within the wires of a circuit. While Esri products have had a network capability for a long time—mainly to deal with transportation systems—the geodatabase takes this capability to new heights. Using the networking features of ArcGIS 10 geodatabases, you can represent and simulate complex and extensive linear, human-built infrastructure—loosely: pipes, wires, and roads.

This new networking capability is facilitated by storing geographic features and their attributes in a database system that is “object-oriented.” Each row represents an object. Objects are described by attributes. But objects can also have ...