How to find vertices that are within polygons in QGIS?

Question

I have a network of edges and nodes located within 3 zones, as shown in the image below:

I want to know, for each node, which zone it belongs to. Is there a way to extract the information?

So that I have a column in the attributes of the vertices with either Zone_1, Zone_2 or Zone_3? (In reality I have a bigger network with many zones, and would like a fast way to recover this information for each node)

Answer 1

You can apply an Intersection (Vector -> Geoprocessing Tools -> Intersection...) using your point data as Input layer and the zonal polygons as Overlay layer. This will add the intersected polygon's attributes to each point (you can also also select specific attributes to keep).

Answer 2

if you doesn't want create a new layer using Intersection tool, you can:

1. create a new field in your point layer and call it as 'fk_id_polygon'

2. writing this formula by field calculator

   aggregate(

   layer:='layer_name_polygon',
   aggregate:='max',
   expression:= "id_polygon",
   filter:= within(geometry(@parent),$geometry) )

the formula retrieve the field "id_polygon" from polygon table and write the value in attribute cell, for only point within polygons.

"id_polygon" field has to be a unique value that identify each single polygon.

After that you can do Join between 'fk_polygon_id' and 'id_polygon'

or instead of use 'id_polygon' you can use 'name' so to associate Zone name directly at your points