How do I perform gap analysis with line and polygon layer in QGIS?
I have 2 vector layers. The first vector layer has line features and second layer has polygon features as in the following images.
I am trying to perform a gap analysis that is cutting the lines at segments the polygons do not overlay the lines in QGIS.
Shapefiles of line and polygon layers are accessible from the following link: https://drive.google.com/drive/folders/11GhQODoPby9SCnp9WcydOBJHVS3O1Lsv?usp=sharing
As your polygon layer has invalid geometries, you have to run first this method of Processing tool (Fix geometries). Both layers (I named Polygons as Polygons_fixed) loaded in QGIS look as follow.
Afterward, you need to run Difference Processing tool with following parameters:
After click in Run, resulting layer looks as follow. I used an opacity of 20 % in Polygons_fixed for corroborating that produced line layer effectively corresponds to lines which do not overlap.
A simpel example cutting the lines not intersecting a polygon using QGIS Virtual Layers.
select p.id, st_intersection(l.geometry, p.geometry) as geometry from test_line l inner join test_poly p on st_intersects(l.geometry, p.geometry) Input a linestring and three polygons.
New virtual layer with linestring intersecting polygons.
