I've several files composed of elements like the one below which I'm trying to make sense of (essentially a very simple microtopography study).

I've vectorised the image with lots of separate lines ending where they intersect with another line. Each of these vertices has been assigned a separate number corresponding to a line, and these lines are in turn arranged into units (so the photo below is of 1 unit composed of 8+ lines composed of multiple vertices).

I'd like to analyse these to look for regularity in the number of lines comprising a unit, does anyone know of doing this? I would use the "Count unique features in polygon" only I'm only using lines.

I'm using QGIS 2.18 Las Palmas


  • Is the unit somehow quantified? With an attribute field on the lines, or a separate polygon layer?
    – kowalski
    Mar 19, 2019 at 11:43
  • yes, there is a separate attribute field for vertice ID, line group and unit, but they are all line fields. I've extracted the nodes into a separate shapefiles and right now I'm wondering if it's possible to work this by counting the individual nodes within the unit
    – stacy
    Mar 19, 2019 at 11:47
  • 2
    What about a Join attributes by Location between lines and nodes, so that each line is line gets the attributes of all the contained nodes. Then, you can use Statistics by categories for the output of the location join, to calculate the frequency of nodes for each unit category
    – kowalski
    Mar 19, 2019 at 11:58
  • I'm having a go at that now, will let you know!
    – stacy
    Mar 19, 2019 at 12:29

1 Answer 1


Ok I found 2 ways of doing this. The first is as described by Kowalski above (thanks!) using Statistics by Categories after joining the intersections and line layers. I also used the Group Stats plugin using my unit field under Rows; and the vertice id field under colomn, adding count. Both techniques gave the same result. enter image description here

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