Ask A Cartographer

crossing roads

February 24 2010 | 4 comments
Categories: Map Data, Symbology

How to avoid ends of single roads meeting centerline of double-lined roads.

### Mapping Center Answer:

There is a cartographic representations solutions that will probably work for you which is to clip the line so it does not extend past the road centerline. What you do is to clip the symbol geometry of the line so that it ends at the road centerline. Note that you will NOT be clipping the actual feature geometry. For this effect, you will need to use the Cut geometric effect. Here is the help topic associated with this topic. However, with this effect, you need to know 1) which features to cut and which not to cut, 2) how far to cut back the lines as all lines will be cut back equally, and 3) which is the beginning node of the line and which is the ending node of the line, as you specify the cut distance for either the beginning the end or both.

If your data are not digitized so that you can determine these three things, which I strongly suspect they are not (as very few would be!), then this effect will not work for you. In that case, the best thing to do would really be to clean up the line geometry. You could apply a universal "cleaning" process to your whole data set (like selecting all the short lines and deleting them), but if there are any cases where a line REALLY SHOULD extend beyond the other road's centerline (e.g., a small cul-de-sac or a short alley), then the universal cleaning routine will eliminate these real data (you may not actually care about that -- I do not know!) So [perhaps a better solution is simply to identify those candidates for elimination and one-by-one inspect them for validity. Once you have determined they are really errors, delete them. Then re-apply your symbology with confidence knowing that the symbology accurately reflects the geography.

There are multiple ways you can clean up the lines - if you need more information about that, please write back to ask us!

further information posted by Kerstin Johansson on Feb 24 2010 8:23AM
Dear sir. Thanks for quick respons but it didn't really solve my problem. The line is not extending past the centreline of the road. Rather it's extending past the edge of the representation of the centreline (double-lined) i.e. 2 lines with an offset of 0.8 an -0.8 respectively to symbolize a highway.
Cased line symbol posted by Aileen Buckley on Feb 24 2010 8:41AM
AHA! I understand now! The solution for you may line in the use of a cased line symbol for the double line road! A cased line symbol is created by making as multi-layer line symbol. Instead of using two lines – each offset in opposite directions – use instead a thicker line under a thinner line. For example, if you use a thicker black line under a thinner yellow line, then you will have a double line road symbol that looks exactly like the one on the picture of the map you sent. You can experiment with the width of the two lines to produce a symbol that you are happy with. You could also use an existing cased line road symbol available in the default ESRI style () or you could edit one of those to modify the color and width of the lines. For example, take a look at the Expressway, Freeway or Toll Road symbols in the ESRI style.

With a cased line symbol, you will lose the ability to see between the two lines of the double line road, but it will mask your line extensions. And cased line symbols are very commonly used to symbolize roads anyway. We wrote a few blog entries about this:

http://blogs.esri.com/Support/blogs/mappingcenter/archive/2007/11/27/symbolizing-roads-with-cased-line-symbols-part-1-of-3.aspx

http://blogs.esri.com/Support/blogs/mappingcenter/archive/2007/11/29/symbolizing-roads-with-cased-line-symbols-part-2-of-3.aspx

http://blogs.esri.com/Support/blogs/mappingcenter/archive/2007/12/06/symbolizing-roads-with-cased-line-symbols-part-3-of-3.aspx

One other thing you might want to look up relative to symbolizing roads is the use of Symbol Level Drawing (http://webhelp.esri.com/arcgisdesktop/9.3/index.cfm?id=299&pid=287&topicname=Working_with_symbol_levels). Using this tool with cased line symbols, you can show a connectivity effect when cased line symbols intersects.
transparency posted by Kerstin Johansson on Feb 24 2010 9:57AM
Thanks again for a new very quick respons. Cased line could be a way of solving the problem. In fact that's what we are using presently in our ArcGIS desktop produced maps. We are though not totally satisfied with cased line symbol for our maps as we are making geological maps and the roads are secondary but important information. It is important to be able to symbolize roads in a way similar to that of a topographical map of the same scale. Cased line roads unfortunately as you say may hide important geological information (point features or even small lines).

I hoped to find a solution for ArcGIS desktop as we were able to solve this problem for maps produced with ArcInfo workstation.

As the topographical dataset is secondary we also want to amend it correctly but with as little work as possible. We would like to have 'rules' that can be applied to a whole dataset without making corrections for each new map.

I will look a bit further into what the possibilites are with using "underpassing masking" as discussed in above mentioed thread: symbolizing-roads-with-cased-line-symbols-part-2-of-3.
Try the masking tools instead posted by Aileen Buckley on Feb 24 2010 10:23AM
Well, the Create Overpass tool won't work for you because your single line roads do not completely cross over the double line line roads. Howsever, you could try the Intersecting Layers Mask tool instead. You will have to first separate your roads into two layers (one for the single line roads and one for the double line roads) then you will need to convert your symbolized roads to represeatations. Then you can use the Intersecting Layers Masks tool with the two rep feature classes as the inputs.

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