5.1.  Abbreviated terms

The abbreviated terms clause gives a list of the abbreviated terms necessary for understanding this document.

Table 1 — Abbreviations

6.1.  Overview

The requirements described in this section define the symbology core requirement class. The UML diagram (Figure 3) shows the fundamental concepts of the Symbology Conceptual Core Model.

Figure 3 — UML Class Diagram of the Symbology core

Table 2 — Requirements Class

Each concept in the model can be extended according to two main extension principles:

• either globally related to an abstract class (in yellow); and

• or locally related to the extension property defined within each class of the model.

The role of each class and property in the model above is described in the tables below.

6.2.  Class Style

This class is the root concept of the Symbology Conceptual Core Model. This class organizes the rules of symbolizing instructions to be applied by a rendering engine on a layer of geographic features (e.g., vector based spatial data or raster data). As an abstract class, it is designed to be extended (e.g., the FeatureTypeStyle extension for vector data).

Please note that the graphic pipeline of the rendering engine must be expressed unambiguously for each concrete implementation of a Style in order to enable cartographic portrayal interoperability.

The StyleClass properties are documented in the following table.

Table 3 — StyleClass

6.3.  Class Rule

This core class describes the concept of a rule in the Symbology model. Rules are used to organize symbolizing instructions and potentially to define conditions of application of these associated symbolizers (e.g., feature-property conditions or map scales).

The RuleClass properties are documented in the following table.

Table 4 — RuleClass

6.4.  Class Symbolizer

This class describes how to portray geographic data given a shape (e.g., area fill, line stroke, point marker, etc.) and graphical properties (e.g., color, opacity, font-family, etc.). As an abstract class, it is designed to be extended.

The SymbolizerClass properties are documented in the following table.

Table 5 — SymbolizerClass

To understand what the symbolizer concept is, consider a “Lake” feature type represented by a Polygon that is to be symbolized as a “blue” filled polygon with its boundary drawn as a “black” line. As symbolizer is an abstract class: a concrete extension called here, for example, AreaSymbolizer, which must be provided to render an interior “fill” and an outlining “stroke.” Consequently, the AreaSymbolizer extension will implement concrete extensions of the abstract Stroke and Fill classes of the conceptual model.

Depending on the type of geographical object, a set of symbolizer extensions can be conceived. For example a LineSymbolizer to draw a river, a PointSymbolizer to represent the “Hospitals,” or a LabelSymbolizer to render the road name along a line.

6.5.  Class ParameterValue

The ParameterValue class represents a gateway that provides the value to be used by a parameter in a styling context of use (almost all styling parameters such as width, opacity, displacement, etc. are “parameter-values”). This class has a similar meaning to Expression as defined in the OGC Filter Encoding 2.0 standard. As an abstract class, it is designed to be extended (e.g., Literal).

The ParameterValue properties are documented in the following table.

Table 6 — ParameterValue

(a) The language identifier should offer a way to adapt the ParameterValue to a specified language, e.g., display the title of a Rule element both in English and French.

6.6.  Class Literal

The Literal class is a concrete implementation of the ParameterValue class. LiteralClass represents a typed atomic literal value as a constant explicitly specified. It was originally defined in the OGC Filter Encoding 2.0 standard section 7.5.1.

LiteralClass properties are documented in the following table.

Table 7 — LiteralClass

6.7.  Class UOM Codelist

For styling parameters that define sizing and positioning of graphical objects (width, displacement, etc.) the unit of measure needs to be provided for the rendering engine. Therefore, for different levels of elements (e.g., Symbolizer, Stroke, Fill, GraphicSize, etc.) the model allows using different uom codes. Consequently, either the unit of measure is determined through the uom code directly associated to each element or it is determined by the innermost parent uom code (e.g., an uom code defined at the Symbolizer level implies that this unit is applied for all sizing and positioning values inside the Symbolizer).

Below is the list of allowed units of measure as per UCUM (except for pixel): * portrayal units: pixel, millimeter, inch, percentage; and * ground units: meter, foot.

The portrayal unit “pixel” is the default unit of measure. If available, the pixel size depends on the viewer client resolution, otherwise it is equal to 0.28mm * 0.28mm (~ 90 DPI).

6.8.  Class Color

The ColorClass allows the definition of color. As an abstract class and part of the base of the core graphical concepts, this class is a global point of extension for specifying concrete definitions of colors (e.g., RGBColor extension).

The ColorClass properties are documented in the following table.

Table 8 — ColorClass

6.9.  Class Fill

FillClass defines the graphical symbolizing parameters required to draw the filling of a two-dimensional shape such as a polygon. As an abstract class and part of the base of the core graphical concepts, FillClass is a global point of extension for specifying concrete definitions for shape fill operations (e.g., the SolidFill and GraphicFill extensions).

The FillClass properties are documented in the following table.

Table 9 — FillClass

6.10.  Class Stroke

StrokeClass defines the graphical symbolizing parameters for drawing an outline (e.g., for linear geometries or the exterior of a polygon geometry). As an abstract class and part of the base of the core graphical concepts, StrokeClass is a global point of extension to specify concrete ways to draw outlines (e.g., the PenStroke and GraphicStroke extensions). The StrokeClass properties are documented in the following table.

Table 10 — StrokeClass

6.11.  Class Graphic

The Graphic class defines the parameters for drawing a graphic symbol such as shape, color(s), and size. A graphic can be informally defined as “a little picture” and can be either a bitmap or scaled vector (the term “graphic” is used instead of the term “symbol” to avoid confusion with Symbolizer, which is used in a different context in this model). As an abstract class and part of the base of the core graphical concepts, GraphicClass is a global point of extension to specify concrete ways to draw “graphic symbol” (e.g., ExternalGraphic and MarkGraphic extensions).

The GraphicClass properties are documented in the following table.

Table 11 — GraphicClass

6.12.  Class GraphicSize

The GraphicSize class determines the size of the graphic when it is rendered. As an abstract class, it is designed to be extended to support the various ways the size could be specified such as by a single value, a rectangular box, or by a three-dimensional cube. The GraphicSize properties are documented in the following table.

Table 12 — GraphicSize

6.13.  Class Label

LabelClass defines the graphical symbolizing properties for drawing a text label. As an abstract class and part of the base of the core graphical concepts, LabelClass is a point of extension to specify concrete ways to draw text label according to placement behaviors (e.g., a PointLabel or LineLabel).

LabelClass properties are documented in the following table.

Table 13 — LabelClass

6.14.  Class Font

The FontClass describes the font properties to apply for the rendering of a text string. It refers to the W3C CSS Fonts chapter.

FontClass properties are documented in the following table.

Table 14 — FontClass

(a) Any number of FontFamily parameters may be given and they are assumed to be in preferred order. (b) The size unit is specified by the uom code if defined or by the innermost parent unit of measure definition otherwise.