Understanding representation rules
This topic applies to ArcEditor and ArcInfo only.
A representation rule contains symbol layers and geometric effects to define how a group of related features in a representation is drawn. Representation rules can be stored within styles for sharing and reuse in other representations. The power of symbolizing features with representations lies in the structure provided by representation rules, which drive the appearance of your data. Representation rules are defined for categories of features in a feature class. They can be automatically translated from a symbolized layer or built from scratch. Either way, representation rules are easy to modify at any time, thereby updating the appearance of all feature representations following that rule.
Creating, deleting, or modifying representation rules requires an ArcEditor license or higher.
A representation rule is built from one or more symbol layers that are defined by their basic symbol type: marker, line, or fill. The basic symbols defined in the symbol layers are applied to the geometry of each feature to display it on the map. Representation rules can be created using only symbol layers, or they can include geometric effects to create complex representations. Geometric effects process the geometry of feature representations before the basic symbol of the symbol layer is applied. Geometric effects can have a global influence so that they process the geometry of features before any symbol layer is applied, or they can reside in individual symbol layers to process only the geometry that is used by that symbol layer to draw.
You can view and modify representation rules from the Feature Class Properties dialog box in ArcCatalog or from the Layer Properties dialog box in ArcMap.
Representation rules are part of the feature class they symbolize. Their definitions are stored and maintained inside the geodatabase along with your geographic data. Changes made to a representation rule while making a map will subsequently appear in all other maps referencing that feature class representation.
The symbol layers in a representation rule define how feature geometry will be displayed on the map. Symbol layers are classified by their output symbol type—marker, line, or fill. The feature geometry must be compatible with this symbol type, or it must be dynamically altered with geometric effects or marker placement styles until it is compatible. For example, to add a fill symbol layer to a representation rule for line features, a line-to-polygon geometric effect (such as the buffer geometric effect) must be included in the representation rule to dynamically create polygons from the line geometry. Otherwise, there will be no polygons to which to apply a fill symbol.
The order of symbol layers in the dialog box dictates their draw order. Use the arrow buttons to reorder symbol layers to achieve the correct appearance. Geometric effects within a symbol layer have no influence beyond that symbol layer.
Fill symbol layers symbolize polygon geometry with one of three patterns:
- Solid—Fills polygons uniformly with a single color
- Hatch—Covers polygons with evenly spaced parallel lines
- Gradient—Fills polygons with a smooth transition between two colors in a linear, circular, or rectangular shape or a buffer that follows the contour of the polygon boundary
Line symbol layers symbolize line geometry and polygon outlines with a solid stroke. They are defined by color, line width, cap type, and join type.
Marker symbol layers symbolize points or locations with a representation marker symbol. Representation markers can be a collection of multiple geometry types grouped together into a single graphic symbol. Use the Marker Editor to modify representation markers, which can then be saved to the Representation Markers folder (not to be confused with the Marker Symbols folder) in a style.
Marker placement styles
Every marker symbol layer includes a marker placement style. Marker placement styles define how markers will be placed in relation to the representation geometry. A marker placement style allows markers to be placed on points, along lines, or in polygons. Each marker placement style has a number of properties that become representation properties available for override when editing with the representation tools.
Geometric effects dynamically alter the geometry of features as they are drawn on your map. This can mean changing the shape of the geometry or even the geometry type. More than one geometric effect can be added to a representation rule functioning in sequence to create complex displays. Geometric effects are characterized by their output geometry type.
Geometric effects can reside in the Global Effects component of a representation rule to define the input geometry for all symbol layers in that rule, or they can exist within a single symbol layer to define the input geometry for that symbol layer alone. A representation rule can have any number and combination of global and symbol layer geometric effects or none at all. Geometric effects act cumulatively within a representation rule such that the dynamic result of one becomes the input for the next.
Geometric effects consist of variable properties that define how the geometry will be formed for display. These properties differ by effect. For example, a buffer geometric effect only includes a buffer size property, but a dash geometric effect contains properties that control the dash pattern, the line cap of each dash, and how dashes will be drawn at ends of line features. Altering the value of any geometric effect property for an individual feature during an edit session creates a persistent override to the representation rule for that feature.
Managing overrides with explicit fields
Symbol layers and geometric effects are composed of properties. Each property has a default value. In addition to this constant, any property can use a field in the feature class to determine variable values. (This field must actually reside in the feature class table itself. It cannot be accessed through a join, relate, or relationship class.) This field, called an explicit representation field, will take precedence in determining the value of the property for each feature. The default value will be used for that property only if the field contains a null value. If you change the value of a field-mapped property for an individual feature during an edit session, the new value will be stored in the explicit field, overwriting the original value.
An explicit representation field can be used in two ways. It can function as a lookup table, storing the results of a process or calculation that are then used to drive display, or it can begin as an empty field of null values to explicitly store changes made during editing. Overrides can then be easily viewed or queried just by examining the feature class table. In comparison, overrides made to properties that use just the default value will be stored in the Override field. This is a binary large object (BLOB) field, so you cannot see or query the overrides stored within it.
Saving and sharing representation rules in a style
Representation rules can be stored and organized within the Representation Rules folder in a style. In a style, a representation rule will contain symbol layers and geometric effects but no geometry. Default values for each property will be stored, but field mapping to explicit representation fields will not be stored.
You can save and load representation rules to and from a style when you create a feature class representation or modify its properties in either ArcMap or ArcCatalog. Since modifying the representation rules that make up a feature class representation is a schema change for the geodatabase, you will not be able to save and load representation rules to and from styles while editing.
You can create, manage, and modify representation rules from the Style Manager dialog box. All representation rules, regardless of the geometry type they are intended to display, will be stored together in the Representation Rules folder in a style. If a representation rule is applied to incompatible geometry in a layer, the geometry logic warning icon will appear within the representation rule. You will need to add, remove, or modify the geometric effects and/or marker placement styles in the representation rule until it is compatible with the geometry type of the data.