Polygons inside polygons QGIS

Question

I am pretty new with QGIS and GIS in general.

The thing is I have 2 shapefiles, the first one with municipalities (2457 polygons) and the second one with hydrological regions (363 polygons). I need to know which municipalities are inside which hydrological region. The shp with the hydrological regions has a column with an ID (HR1, HR2, etc.).

How can I add that value to each municipality?

Answer 1

You can use Vector general > Join Attributes by Location tool in Processing Toolbox(Ctrl+Alt+T).

1. Set Input layer to municipality layer
2. Set Join layer to hydrological regions layer
3. Select within only
4. Select only ID field in Multiple selection window
5. Set Join type to Take attributes of the first matching feature only (one-to-one) and run the tool

Answer 2

You can use the tool join attributes by location : https://docs.qgis.org/3.10/en/docs/user_manual/processing_algs/qgis/vectorgeneral.html#join-attributes-by-location

He is located in the tab Vector -> Data Management Tool

It allows you to choose 2 layers and the spatial relation to join attribute from one layer to the other (intersect, touches, within, etc...). You can also choose the column to join.

In the pictue layer_A will be your municipalities, layer_B your Hydrological Regions and the Geometric predicate is within. So every municipalities obtain the ID of the Hydrological Regions they are in.