Ask A Cartographer

"Phantom" circles

November 30 2007 | 0 comments
Categories: Map Data, Symbology

When I began working in Geodatabases and creating real curves, I ran into a problem when symbolizing those lines with curves. "Phantom" circles began appearing which were coincident with the curved portion of the "real" line. Experimentation shows that these phantoms only occur when using certain line ymbols, such as "Automobile Tunnel", "New Road Under Construction", and "Existing Road Under Construction".

I have attached a picture illustrating this curiosity. Note that the phantom circles are not drawn using the symbol selected as they should.


Attachment: Example of "Phantom Circles" in GDB w/real curves

Mapping Center Answer:

This is a known limitation with offset line symbols (if you look in the properties of the symbols you listed, you’ll see they’re composed of two lines that are offset to either side of the feature’s geometry).

One workaround that I have some, but not an overwhelming amount of confidence in, but worth mentioning because it is the least amount of work; is to convert your lines to representations. In 9.2, however, you may still see some phantom circles. You can add the simplification geometric effect and that may fix things, but as you increase the amount of simplification the trade-off is the quality of your curves. There is some good news long-term, which is that with the problem in mind, we made some changes to the way representation offset lines work for 9.3 and have fixed the issue for representation lines.

There is another way to accomplish the same effect, and still use curve geometry. Symbolize your lines with a railroad style line where hash is slightly wider than your current line symbol and the interior line is slightly narrower than your current line. Use Feature Outline Masks tool to create masks of this line. Then draw your lines with just a wide line (no dashes) and use the variable depth masking feature (right-click on the data frame and choose Advanced Drawing Options to get started). One tip here is to convert the railroad line to representations before creating masks so you can create a higher quality pattern of hashes (use the control points geometric effect).

If you would like to post a comment, please login.

Contact Us | Legal | Privacy |