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I have two feature classes: point and polygon. The purpose is to make geometrical relations between them. For instance, if points are within a polygon then automatically make the relation between polygon and point and to see all polygon information in point attributes, but I don't have identical ID's.

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    – PolyGeo
    Jun 21 at 8:50

2 Answers 2

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You can use this expression:

array_to_string (
   overlay_within (
      'Polygons_layer', 
      Attribute_Polygon_you_want
   )
)`

This is for "completly within", but there are other "overlay" expressions, see https://docs.qgis.org/3.22/en/docs/user_manual/expressions/functions_list.html#overlay-contains.

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Does "Join by localisation" not fit your needs? Select "point layer" as source, "intersect" as predicat and "polygon layer" as layer to join.

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  • No, because it creates a new vector layer which is an extended version of the input one. It needs to be in the same feature with automatic updates. Jun 21 at 9:39
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    you can create a new field (virtual or not) in your point layer with the expression: aggregate(layer:='Polygons_layer',aggregate:='concatenate', expression:="Attribute_Polygon_you_want", filter:=intersects($geometry, geometry(@parent)))
    – katagena
    Jun 21 at 10:12
  • Thanks a lot, it really worked for the points on update! could you please tell me how to do the same for lines if they are within(or completely within) the polygon? Jun 22 at 6:14

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