I have a shapelayer with lines (streets), each line has a value for the traffic on it. The value is shown by the width of each line. Now I want to smooth the transition between one segment that has e.g. the value 500 which goes into a segment with value 100. Any ideas? I want to achieve more or less the same result, as in this post, only automatically for a larger dataset … Blend differing line thicknesses in QGIS?

Maybe a little graphic helps: Above what I got. Bottom, what I want to have. Each line segment has only 1 value, and I want to smooth the segments into each other. enter image description here

  • Is there a reason the linked post wouldn't work for your situation?
    – jcarlson
    Mar 5, 2018 at 13:07
  • Yes, as stated I need this to work automatically for a large dataset. If it was only for single lines, I would do it in Illustrator, but I need it for a whole Street Network … Mar 5, 2018 at 13:08
  • If the arrow size is determined by the same value as the width, this can be applied to the entire network via layer styling options.
    – jcarlson
    Mar 5, 2018 at 13:14
  • Why not do this with rule based styles mimicking what the other post shows?
    – artwork21
    Mar 5, 2018 at 13:18
  • It sounds to me, as you somehow know the solution – I just really dont know the HOW. How can I "tell" one line, to "look out" for the next line (which doesn’t have an attribute, saying it is the next line) and scale in width accordingly? Mar 5, 2018 at 13:30

1 Answer 1


This is not a complete solution, but it may provide a starting point that you can improve on.

Use an arrow symbol type. Add two numerical fields to your street layer: startwidth and endwidth. Use these fields to control the arrow width and arrow starting width. enter image description here

The startwidth of each line feature should be the same as the endwidth of the line it connects to.

enter image description here

enter image description here

In my test example, I filled in the values for startwidth and endwidth manually. The next question would be how to automate these values.

  • Yes, great, thank you! Definitely a starting point! … any ideas about automatization anyone? Mar 6, 2018 at 8:50
  • I think if you use a data type other than shapefile, there are ones where you can define have lines "know" that they're connected to each other. Concepts to look into would be topology and networks.
    – csk
    Mar 6, 2018 at 17:03

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