BorderMergeOperator.Attributes Property
Gets a list of attributes, whose values must be copied from input polygons to output lines.
Syntax
public StringCollection Attributes { get; }Property Value
Default: Empty collection.
A list of attributes, whose values must be copied from input polygons to output lines.
Remarks
Since each output line can get attribute values from two or more input polygons, the attribute names of the polygons cannot be reused for the lines; the attributes from different polygons must be distinguished.
Let us see what happens if "NAME" appears in the attribute list.
First, we assume that the polygons are of same type (for example, countries) and do not overlap. Then, we do not need any prefix. The border between France and Luxembourg will get the attributes
NAME_L: "Luxembourg"
NAME_R: "France"
assuming that the border is drawn eastwards. The "_L" suffix refers to the polygon on the left side of the line, and the "_R" suffix refers to the polygon on the right side of the line. Left and right is relative to someone who walks along the line from its first point to its last.
Now, let us assume that polygons are of two types, countries and regions, which overlap. Both the country polygon for France and the region polygon for Lorraine are to the right of the French-Luxembourgian border. If we do not use any prefix, the border would get the attributes
NAME_L: "Luxembourg"
and either
NAME_R: "Lorraine, France"
or
NAME_R: "France, Lorraine"
As you see, the values of conflicting string attributes will be concatenated. For an attribute of another type, an arbitrary value will be chosen among the conflicting ones. Therefore, it is better to use the AttributePrefix. If you can let the prefix evaluate to "COUNTRY_" for country polygons and to "REGION_" for region polygons, the border would get the attributes
COUNTRY_NAME_L: "Luxembourg"
COUNTRY_NAME_R: "France"
REGION_NAME_R: "Lorraine"
The prefix also makes it possible to display country borders with a different LineVisualizer than region borders. The country borders will have a COUNTRY_NAME_L or a COUNTRY_NAME_R, or both. The region borders will have neither a COUNTRY_NAME_L nor a COUNTRY_NAME_R.
In the examples above, we assumed that the French-Luxembourgian border would be drawn eastwards. But since you cannot predict the direction of a border line, you must design your text visualizers so that the direction is not important. For the text to follow the line, your TextVisualizer should have a rotation of -90 degrees, and rotation mode FlipUp. Labels that should appear on the left side of the line (from attributes ending with "_L") need a negative PointVisualizer.OffsetY, and labels that should appear on the right side of the line (from attributes ending with "_R") need a positive PointVisualizer.OffsetY. We would also recommend using Middle.
Platforms
Windows, Linux, Android