Project: QGIS
Version: 2.12.0
This allows users to set a layer as just an obstacle for other layer's labels without rendering any labels of its own. It means that a non-labelled layer can act as an obstacle for the labels in other layers, so they will be discouraged from drawing labels over the features in the obstacle layer, and allows for improved automatic label placement by preventing overlap of labels and features from other layers.
In the screenshot you can see that the Streets have the option "Discourage other labels from covering features in this layer" enabled. The red labels derived from polygon geometries are thus placed to avoid intersection with the street axis. You have to enable "Horizontal" or "Free" on the polygon layer in order to achieve proper results.
Note, that it is also possible to both label a layer, but also act as obstacle layer, by enabling the checkbox "Discourage labels from covering features" in the "rendering" tab of the label settings.
See this article for more details.
This feature was developed by: Nyall Dawson
