A quick, clean method for insetting polygon outlines

By Charlie Frye, Esri Chief Cartographer

Example of inset boundary lines

Quite some time ago we posted a blog entry on creating tint bands, which are bands of color either interior or exterior to polygons along their borders.  You will see this cartographic effect on world atlases, for example, using different colors to distinguish the various counties. The solution we presented was involved and complex, but it did preserve essential characteristics of the polygons better than any other method we tried.

We were recently asked about a similar problem; the purpose was to help readers visualize which areas of the screen were within which polygons while possibly showing additional background data, and do so with without any ugly drawing errors. We needed to provide a solution that avoided problems that occur when just setting an offset for line symbols (click on the image below with the red outlines to see a detailed view of the problems that can occur.

Quick Clean Polygon - Figure 1

Quick Clean Polygon - Figure 2
After a bit of testing, it turns out that there is a simple way to use cartographic representations symbology to create this effect, and the same solution can be used for the tint bands that were introduced at the beginning of this blog entry (if you don’t mind the rounded over look of the buffers, in fact you may prefer it). The Donut polygon effect with the True buffer method (Simple) did the trick.

The only caveat is that it definitely slows down drawing performance.  But this method has the added benefit of on-the-fly clipping of the buffers to the original geometry, so none of the problems illustrated in the example of the red offset lines shown above occurred.

We also found that the Simple option improved drawing performance slightly without causing defects in the resulting line-work.

It should be noted that none of the other representations symbology methods for either the Donut effect or the Offset curve effect produced the same clean solution for an inset line.

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One Comment

  1. spardo2 says:

    Hi, I realize this post was made 5 years ago so perhaps my inquiry will go unnoticed, but here it is anyway.

    Where do we find the donut polygon effect in ArcMap 10.0?

    I can’t seem to navigate to that last screen grab of the donut tool. I’ve tried following the documentation provide with 10.0 found here:
    http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#/Creating_new_donut_holes_and_island_polygons/001t0000003p000000/

    Yet, it does not appear to have the same functionality and ease of implementation.

    Please advise!