SPATIAL DATABASES

In the field-based model of the space, each point has one or more attributes values that are typically defined by continuous functions. In other words, there is a mapping from space to a value of an attribute. For example, vegetation may be modeled as a function where the domain is the space and the range is the value of type of vegetation. The function is constant in the space with the same vegetation.

To specify a field-based model involves the determination of three components (Worboys 1995):

• Spatial framework , which defines a finite grid imposed over the underlying space.
  
• Field functions, which map the spatial framework onto attribute domains.
  
• Field operations, which map a subset of fields onto other fields. Field operations can be further classified into local, focal and zonal operations.The decision to use an entity-based model or field-based model depends on the requirements of the applications. Many geographic phenomena, such as flood, pollution, and fire are commonly modeled as fields. Likewise, some continuous spatial trends, such as temperature, elevation, and all related topics to remote-sensing applications use a field-based model. An entity-based model, in contrast, is commonly used in application related to man-made spatial objects, such as transportation networks, cadastral application, and land-ownership application.