I would like to style a polygon layer in a way that only those borders that do touch other polygons are drawn.
In this very basic example, it would look (roughly) like this. Just that in this case I drew the lines;)
The idea is that I want to draw the borders between countries, but not the coastlines. The example QGIS Project can be downloaded from here.
Use Geometry Generator with this expression (alternatively, you could also use intersection() instead of shared_paths() function):
collect_geometries(
array_foreach(
overlay_intersects (@layer, boundary($geometry)),
shared_paths (@element, boundary($geometry))
)
)
I applied the Geometry Generator to a duplicated layer of your polygon layer:
boundary($geometry) as an expression? And what does it exactly do in this context? Couldn't I just use $geometry?
$geometry here is a polygon. We want lines instead. That's why I used boundary($geometry) to convert the polygons to lines, the outer boundaries.