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I have a map with 'Layer A' (polygons representing cities) and 'Layer B' (lines representing roads).

I would like to add a virtual field on my 'Layer B' table with the name of every city crossed by each road.

enter image description here

In this example, I would like my Road 1 attribute to tell me it crosses 'City A', 'City B', 'City C', and 'City D'.

Is this possible with a QGIS expression, within a Virtual Field?

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2 Answers 2

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Try this expression:

array_to_string(overlay_intersects('Layer_A', name))

(assuming the City names are stored in name field in the 'Layer A').

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  • Thank you, this works as expected !
    – Arthur
    Commented Oct 1, 2021 at 7:25
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Currently a bit "old-fashioned" approach using the aggregate() function:

aggregate(layer:='Layer_A',
          aggregate:='concatenate',
          concatenator:=',',
          expression:="name",
          filter:=intersects($geometry, geometry(@parent))
          )
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  • What is the length of the road segments through these areas of cities?
    – Frodo
    Commented Oct 7, 2021 at 11:55
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    A good question and I think it deserves a new question (perhaps it was already asked before). However, this solution may help you: expression:=to_string("id") || ':' || to_string(length(intersection($geometry, geometry(@parent)))) results in length for each feature separately, if sum required then aggregate:='sum' and expression:=length(intersection($geometry, geometry(@parent))).
    – Taras
    Commented Oct 7, 2021 at 12:55

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