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ESRI Lunch Specials: Using representations to symbolize railroad hashes
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Railroads symbolized using default railroad symbol.
Railroads symbolized using default railroad symbol from with just a color change to gray.
The same railroad lines symbolized with representations where the spacing of the hashes could be adjusted.
The same railroad lines symbolized with representations where the spacing of the hashes could be adjusted.

What: When we evaluated an initial draft of this map, we saw that the railroads were so unorganized looking that they detracted from the overall effect of the map. We needed to keep them on the map as the railroad is a prominent feature that must be crossed to enter the Gaslamp district.

Why: To create cartographically superior railroad lines the goal is to align the railroad ties (the hash lines that cross the main line symbol at intervals). The default symbology didn’t work because different railroad lines started and ended at different locations. To make the map on the right (above) we used representation symbology (new in ArcGIS version 9.2) where we manually added control points the representations in an edit session; this provided a complete definition for where the railroad ties should be drawn.

How: We followed these step to create railroad lines with representations:

  1. A key change was made to the railroad data, where we added an attribute that differentiated whether the line was a main line or just a connector. The symbology for the connectors was then changed to be just an unadorned line with no ties.
  2. We created representations by right-clicking on the layer in the table of contents and choose Convert Symbology to Representation.
  3. To add control points to align the railroad tie symbols we did the following:
    1. Choose Start Editing from the Editor toolbar.
    2. In the Table of Contents' Selection tab, we made the layer that used the representations we created in Step 2 the only selectable layer.
    3. We selected the railroad line with the ties that least conformed.
    4. We opened the Representation toolbar and used the Insert Control Point Tool and clicked where we wanted the center of the gap between railroad ties on that line (the default option for this representation is to start the pattern of hashes with a half gap, so that is the rationale we used for clicking where the center of the gap). We found it took a little practice, and we used the Undo button on the Standard toolbar as often, working until the hash marks lined up exactly where we wanted them. We also zoomed in a great deal, often isolating just a few ties.
    5. We continued adding control points until the railroad ties were placed in a visually pleasing fashion.

We also found that some railroad data contains short segments that will not support drawing the full railroad tie symbol pattern. We selected these segments with other coterminous lines and use the Merge option from the Editor menu to create longer, symbolize-able lines. Note that this may require you to use a copy of the railroad data in the map if merging features will result in unwanted loss of other attributes or data.

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