I downloaded some road network data derived from OSM by GeoFabrik, see the initial state: Near Székesfehérvár (Hungary) Near Székesfehérvár (Hungary), parallel lines are probably trunk or motorway roads.

I would like to simplify it like this (drawn in Paint): enter image description here

I would like to use open source stuff for that (QGIS, GRASS), so I tried v.clean and v.simplify, v.generalize in some combination. Unfortunately, I cannot reach the desired result.

With v.clean 'snap' method, tolerance=50 I reached this:

After v.clean snap.

But I don't need duplicated geometries, or identical zig-zag lines. Probably the v.generalize.network (Closeness, Betweeness threshold) would solve the problem, if it worked.

You can download the clipped geodata here: https://github.com/ewirth/gistemp

2 Answers 2


Buffering the road may be a solution to this problem.

  • create a dissolved buffer of the road using around 20 unit map distance. enter image description here

  • import the layer into a postgis database and create the middle line using ST_ApproximateMedialAxis() function:

SELECT ST_ApproximateMedialAxis(geom) AS geom INTO road_centre_line FROM road_buffer;

  • in order to access this function you have to enable the postgis_sfcgal extension
  • with this you will get an output like this enter image description here

For this question in my experience, Toolbox in ArcGIS can solve this problem. You can use the Merge Divided Roads tool under the Generalization tool in Toolbox.

In details: Firstly, open the attribute table of your map in ArcGIS, add a field named it as add and then use field calculator to let add=1

Secondly, use the Merge Divided Roads tool under the Generalization tool in Toolbox by different merge distance, such as 60m. This step should repeat several time by using different merge distance, such as 60m, 30m, 60m, 30m.

Thirdly, use topology check to deal with pseudo nodes in the road network. Pseudo nodes are nodes that are not located at line intersections and it occur where a single line connects with itself or where only two polylines intersect. For topology check you can find processing in the following linkage: https://sites.google.com/site/ochaimwiki/geodata-preparation-manual/how-to-check-topology-using-arcgis

Hope my answer is useful for you.

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