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3 Non-geometry standards
and it eontains one or more seareh eriteria based on a parameter eombination that
may include map type, feature type, feature class, or seale range.
Examples of topographie feature types are streams, fields, and elevation points. A
portrayal eatalogue eontains one eartographie representation for eaeh feature type.
For these examples it may eontain a blue line for streams, a green fill-area symbol
for fields, and a brown point for the elevation points.
The portrayal speeifieation eontains all the attributes and operations required to
derive the graphie representation for the given feature type aeeording to the applieable rule. The eatalogue will always speeify adefault representation if the rule-seareh
for a given feature type fails.
In order to adapt the graphies to any given symbolisation eatalogue, external funetions may be applied to the individual rules or to the whole dataset. An example is a
ear navigation system that will always display the map with the driving direetion up.
Dense graphies may result in an uneontrolled overlay of the elements. A priority
attribute allows defining the top element that hides the others in the ease of multiple
elements at the same position.
More than one feature eatalogue may be defined for one dataset in order to allow
for different types of maps.
Dataset
Portrayalcatalogue
Ft!ature
portray
portrayed by
FeaturePortrayal
Ln
Ln
used In 1 .. n
lies Ln
ExternaIFunction
Portr.!yalRule
used In 1 . .n
uslng 1 .• n
PortrayalSpecification
Fig. 3.16. Portrayal of a feature using a portrayal catalogue (IS049 2002)