In sections 2.1 and 2.2 we have looked at the way maps are stored and displayed in
ILWIS, either as point, segment, polygon or raster maps. In the sections 2.4 up to and
including 2.6 we have also looked at the service objects that contain information
about these maps, such as a domain, a representation, a coordinate system and a
georeference.
In section 1.3 we have also seen that spatial data (maps) can be linked to non-spatial,
or attribute data (tables). In order to be able to link a map with a table, the units of a
map must be linked to records in a table. The attribute information can then be added
in columns. In other words, a map and its attribute table should use the same domain.
Let us briefly check this again.