Creating Atlas dynamic text from multiple layers in QGIS

Question

I am creating an atlas using QGIS v3.12 but would ideally like to include a dynamic text box that takes values from multiple layers contained on each atlas feature page.

The map is made up of two layers ('zones' & 'networks') 'zones' used to generate the atlas, but I'd like to include some of the attributes from 'networks' including 'total_properties'.

I've tried using:

aggregate(
layer:='networks',
aggregate:='concatenate', 
expression:="total_properties",
filter:=intersects($geometry,@atlas_geometry),
concatenator:=','
)

But it returns the error "Eval Error: Could not calculate aggregate for: total_properties".

It only seems to work if the attribute name is common with the 'zone' layer (they are different geometry types from different sources but have some common attributes). I even created an attribute table for 'networks' and copied the attribute names from the expression builder to ensure they're spelt correctly.

Answer 1

This is probably because your total_properties field is numeric and concatenate only works on string data types (why QGIS doesn't autoconvert numeric values for this is beyond me - perhaps in a future release).

Try using expression:=to_string("total_properties") in your expression and see if that works.