Ask A Cartographer


April 06 2011 | 0 comments
Categories: Cartographic Representations, Symbology

Is there a way to create overpasses, where the underlying objects are polygons and not lines? This link shows the effect that someone has already come across:

If this is the only outcome, how easy is it to edit the resulting parapets and masks to stretch along the width of the polygon?


Mapping Center Answer:

This is a really interesting question as the overpass (and underpass) tool is designed to work where one line feature class crosses another.  The tool does not work when a line feature class crosses a polygon feature class…though the following steps provide a workaround to achieve the effect of having the mask and parapet cut across polygons.  The process does involve some manual work and you need to remember that it is dependent on using Cartographic Representations (so all data has to be in a geodatabase).

First, you will need to convert any polygon boundaries of the input below features that you want the above feature to cut through into a line feature classes.  This is done using the Feature to Line tool.  You then convert the resulting line feature class symbology into Representations.

Once your feature class symbology is converted to Representations then you can go ahead and run the Create Overpass tool which will create parapets and masks anywhere that the features above cross the lines of the features below. In your case, you will effectively be creating overpasses across the boundary lines of the polygon. As a result, you will get one set pf parapets where the input above feature enters the polygon and another where it leaves the polygon.

Next, convert your new parapet and mask feature classes to Representations. Do this for both feature classes and remember to check the "Change the Geometry of Supporting Features" in the Convert Symbology to Representations dialog box.  This will cause any future edits to be applied to the feature geometry directly rather than the symbology representation – it's important so that the masking will work properly at a later stage.

Because both the parapet and mask layers are multipart features, in order to be able to edit them individually you now need to convert them to singlepart feature classes using the Multipart to Singlepart tool.  This creates two new singlepart feature classes that also retains the Representations.

Now you can do some manual editing so start an Edit session and make sure you have the Representation toolbar visible and that only the two parapet and mask representation feature classes are selectable (to reduce the possibility of editing other data). Using the Direct Select tool on the representations (or the Lasso Direct Select tool ), select one of the parapet and mask combinations (e.g., where it crosses out of the polygon) and delete them.  Now, turn your attention to the other pair of parapet and mask features and select ONLY the vertices of one end of the features.  You should capture two vertices on the mask layer and four on the parapet layer.  Then, you can hover your mouse over one of the vertices, hold the left button and drag the selected vertices to the end of the polygon where the previously deleted pair of features were located.  Release the mouse and you should have created a longer parapet and mask combination.

Once you have done your manual edits, save the edits and exit your Edit session. The final step to achieve the desired effect requires you to use Masking.  To do this, right-click the data frame and select Advanced Drawing Options.  Here, check the option to "Draw using masking options specified below". Then set the masking layer to be your edited mask layer and set the original polygon feature class as the masked layer (plus any other layers you wish the mask to cover).  You can now deselect the polygon boundary line feature class and the mask layers in the Table of Contents and you should see that you have created overpass symbology that cuts across a polygon.

Note that this process works where you have straight lines across a polygon.  If you have curved lines and require a more complex mask and parapet symbology the process is the same except you will need to do more manual editing to add new vertices to the mask and parapet features and shape it according to your input above line feature class.

This workaround should help you create overpasses for line over polygon situations but if this is a technique that would be more useful as part of the standard overpass tool then please request the tool to be developed by posting the request on the ArcGIS Ideas web page - or check to see if someone else has already suggested this and vote to support it so that the idea receives higher priority.


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

Contact Us | Legal | Privacy |