Using polygons to show dashed-line boundaries; note the dash pattern is not consistent when the lines of adjacent polygons overlap
Using lines that are the result of the Polygon to Line tool to show dashed-line boundaries
What: You sometimes want to convert polygons to line features so that you have more control over the way they are symbolized. Why: If you use a dashed line symbols for polygon outlines, the symbols for adjacent polygons will lay on top of each other -- this is called over-striking. When this happens with lines that have a dashed pattern, the dashes will not line up in most cases, so the line pattern becomes inconsistent and confusing to the map reader. Because we often want to use dashed lines for political boundaries (a common cartographic convention), we need to find a solution to the over-striking problem. Converting the polygons to lines is one way to go. An added benefit of using lines is they draw a little faster because less information is being read from your database and drawn on your screen. To learn more how to make effective choices for line symbols, see pages 152-153 in Designing Better Maps.
TIP
Before you follow the instructions for creating your own boundary lines, the ESRI Data & Maps set of data includes boundary lines for the countries and sub-administrative units (like states & provinces) for the world, so you may not need to create your own when you can use ours.
How: To create boundary lines that can be symbolized with dashed patterns:
- Use the Polygon to Line tool to convert your polygons to boundary lines.
- Add a new field to the boundary lines you just created. We made ours a string field called Bny_type.
- Select the lines that will represent one kind of boundary lines.
- Calculate the values of the Bny_type field to a string that represents the kind of lines you have selected.
- Repeat steps 3 and 4 for each type of line you have.
TIPS
- Be careful in step 1 not to use the Feature to Line tool, which will produce a complete outline of each polygon, effectively recreating the problem with lines instead of polygons.
- We have also documented another effect that deals with integrating coastlines with boundary lines like those covered in this effect.
- With ArcGIS 9.2, try converting your boundary line layer's symbology to representations, so you can also control how the dash pattern starts and ends for each line feature.
If you've got a small dataset, it's probably faster to create a new line feature class and trace your polygons using the editor. For instance, you could do a dataset the size of the U.S. States in less than an hour. To my thinking that's likely the fastest way and I think fewer human errors will creep into this workflow. The other way is to write your own version using Python; in this case, it would be a fairly complex algorithm.
If you're short of time and have a large polygon dataset, try contracting the job out to somebody who has an ArcInfo license.
http://arcscripts.esri.com/
That allow you to find tools for arcview that mimic arcinfo only tools. It's really easy to find things you need so that you can try and solve problems yourself.
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I don't have an ArcInfo license to use "Polygon to Line tool", what would you suggest? Using Convert Polygon to Polyline from ET Geowizards, I end up with 2 border lines for the polygon, as the Feature to Line tool, and not solving the cartographic aspect of dashed lines...