Generating polylines where polygons of two different layers meet in QGIS

Question

I am fairly new to QGIS and just now encountered my first obstacle that i can't solve simply from checking questions already posted here.

For my current study project i would like to highlight the lines along which two different polygons meet. I understand that this can probably be done with vector -> geometry, ->analysis or making use of buffers with fixed distances. However, i just cant seem to find the right option.

Here's my project with two different layers consisting of the clc 10 dataset. Basically, I would like to have lines drawn where the red and green polygons are directly adjacent to another. These lines would ideally be in a new layer.

To give you an idea of what im looking for: In this example green lines are drawn wherever two different layers are directly adjacent to each other.

Answer 1

First convert the red layer to lines (vector > geometry tools > Polygons to lines). This will give you the boundaries of the red polygons.

You can then run vector > geoprocessing tools > clip on the resulting lines and the green layer. This will clip the boundaries to sections that touch the green.

Depending on how the layers are topologically, you may need to buffer the green layer by a small amount and then clip to the buffered layer, rather than the original green.