Geographic Information Systems Stack Exchange is a question and answer site for cartographers, geographers and GIS professionals. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I need to clean a roadmap shapefile to replace all dual carriageways (DCs) with single lines. The Feature to Line tool nearly works, but is destroying some of the road links. My current workflow (since the tool doesn't discriminate between lines of different attribute) is based on a strategy of splitting the shapefile into two - one with the DCs and roads they link to to process, and another with everything rest to be rejoined at the end. Specifically:

  1. use a buffer Select Layer by Location to identify all roads within 1 meter of a DC
  2. create new DC layer from selected features
  3. apply Feature to Line tool to the DC layer with an approx 25m XY tolerance (max distance between carriageway lanes)

However I'm finding that the new simplified DC line objects (typically the roads that linked to DCs) do not properly match up with their continuations in the untouched layer. To illustrate:

enter image description here

Very grateful for any suggestions on how to approach this so the links with the grey roads are maintained. Thanks in advance.

share|improve this question
If on Advanced License (ArcInfo level) you can use Collapse Dual Lines To Centerline (Cartography)… – Mapperz Apr 9 '13 at 17:15
I would seperate your Dual Carriageways to a separate featureclass and work on that layer to stop your lines breaking – Mapperz Apr 9 '13 at 17:18
Thanks guys. My problem here is that many side-roads just link to one side of the the carriageway, so they'll be disconnected from the new centreline. How might I approach an arcpy solution, e.g. by reverting the unconnected nodes of side-roads to their original values? – geotheory Apr 10 '13 at 10:51
Have you used Topology in ArcGIS before?… if the tolerance is correct your lines should snap back to the node. – Mapperz Apr 10 '13 at 13:26
But won't that also snap lots of other roads to the dual carriageway that weren't connected before? – geotheory Apr 11 '13 at 9:05
up vote 0 down vote accepted

Workflow underway along the lines of @Mapperz comments above

share|improve this answer
Be sure to write your workflow up within your Answer once you know it works. – PolyGeo May 22 '13 at 10:37
Certainly shall – geotheory May 22 '13 at 10:56

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.