Joining attributes by the biggest overlapping areas in QGIS

Question

I have two layers and I want to join the attribute of them together in QGIS. Unfortunately, the overlapping layer (The Blue one) is not very precise, so there are parts that overlap on small areas.

If I join the attributes together (-> join type: intersects/one to many), I get multiple overlapping attributes. But i only want the attributes with the biggest overlapping area, which would be those:

If join the attributes together with the one to one method, I often get the attribute of the small overlapping parts, which i don't need/are wrong. I know I can get the mean attributes of all overlapping areas with the "Join Attributes by Location (summary)" function, which is partly a solution to my problem.

But what I really want is to only join the attribute with the biggest overlapping area. Any idea how to do this?

Answer 1

Since QGIS 3.12 (see the Changelog for more details) the "Join Attributes by Location" algorithm from the Processing Toolbox (Ctrl+Alt+T) has a switch to do exactly this:

The type of the final joined layer. One of:

0 — Create separate feature for each matching feature (one-to-many)

1 — Take attributes of the first matching feature only (one-to-one)

2 — Take attributes of the feature with largest overlap only (one-to-one)

Answer 2

In QGIS there is a plugin called "Select Within".

But building on that I developed my own model to join based on the layer centroids by converting the layer to centroids and then join that table... Works a treat.