2-7 Thematic Data Modeling

The real world entities are so complex that they should be classified into object classes with some similarity through thematic data modeling in a spatial database.

The objects in a spatial database are defined as representations of real world entities with associated attributes.

Generally, geospatial data have three major components; position, attributes and time. Attributes are often termed "thematic data" or "non-spatial data", that are linked with spatial data or geometric data.

An attribute has a defined characteristic of entity in the real world.

Attribute can be categorized as normal, ordinal, numerical, conditional and other characteristics. Attribute values are often listed in attribute tables which will establish relationships between the attributes and spatial data such as point, line and area objects, and also among the attributes.

Figure 2.9 shows a schematic diagram of thematic data modeling.

Spatial objects in digital representation can be grouped into layers as shown in Figure 2.10.

For example, a map can be divided into a set of map layers consisting of contours, boundaries, roads, rivers, houses, forests etc.