How To: Use topology to create line features from polygon outlines that can be symbolized as cased or dashed


ArcGIS 8.3 now provides an easier method to outline polygons with either a cased line (a line with fill color and a different outline color), or a dashed or dotted line.
[O-Image] Example of cased and dashed polygon outlines

In prior versions of ArcGIS, problems came from the fact that polygons have shared edges drawn twice, so cased lines did not intersect well, and dashed or dotted lines displayed irregular, overlapping dash or dot patterns.

In ArcGIS 8.3 and later versions, topology is used to create cased and dashed polygon outline features. Instructions provided below are for creating both cased and dashed outlines.


  1. Create a Geodatabase topology in ArcCatalog with at least two feature classes:
    1) a polygon feature class with features, and
    2) a line feature class with no features.
  2. Add the rule 'Boundary must be covered by'. This mandates the polygon outlines be covered by features in the line feature class.
  3. Validate the topology.
  4. Open ArcMap, if not already open, and verify that the topology layer, the polygon layer, and the empty line layer are added. Start Editing.
  5. Double-click on the symbol for your line layer in the Table of Contents. Choose a cased, dashed, or dotted line and click OK.
  6. Open the topology Error Inspector and search for errors related to the 'Boundary must be covered by' rule.
  7. Select all of the errors, then right-click and select Create feature. This creates line features in the line feature class completely covering the boundaries of the polygons.
    [O-Image] Topology Error Insp Create Feature
  8. If symbolizing the lines as cased, turn on Advanced Drawing Options for the line layer in ArcMap. Do this by right-clicking on the data frame and selecting this option from the menu. In the Advanced Drawing Options dialog box, check the box at the top and be sure to set Join = Yes as the line symbol.
  9. Select all of the features in your line feature class and click the Planarize command on the Topology toolbar. This tool requires an ArcEditor or ArcInfo license.
    [O-Image] Planarize tool

    This is the selection used if symbolizing lines as dashed or dotted. Stop Editing and save the edits.
  10. Stop Editing. Save the edits.
  11. Features in the line feature class have been created that can be effectively symbolized as either cased or dashed.