Object properties and dependency links
As shown in preceding sections, different data objects (point, segment, polygon
and raster maps) and service objects (domains, representations, coordinate
systems and georeferences) are required to form a map in ILWIS. How does
ILWIS know which objects are linked?
The properties of an object show which service objects are used for a data object
or another service object. In section 2.2 you saw that for the display of vector
maps, you need to have a coordinate system, a domain and a representation
(depending on the domain) and that a raster map requires the same objects, plus
the georeference. In section 2.7 it was shown that class and ID maps could also be
linked to attribute tables.
In Figures 2.4 and 2.5, a schematic representation is shown of the properties of
vector and raster maps. The properties of vector maps with a class domain,
identifier and value domain are shown in Figure 2.4.
The objects indicated in the shaded boxes are the data objects (i.e. point, segment,
polygon maps and tables) and the objects outside of these boxes are the service
objects. The arrows indicate the relations between the objects. For example, in
Figure 2.4, a domain is used by a vector map (either a point, segment, or polygon
map), by a table, and by a representation.