Avoiding buffer exceeds layer boundaries in QGIS

Question

I generated random points within my map in QGIS. Then I created a buffer zone of 5km around each point because it is necessary for my analysis.

However, now the buffer zone crosses over the layer boundaries which I don't want to happen. Is there any way to avoid this? I want the buffer zones to not intersect with the layer boundaries.

Answer 1

This would be a two step process.

Once you have generated the buffers you can clip them to the boundary.

This can be done with:

Vector > Geoprocessing Tools > Clip

Answer 2

This is a combination of the "Buffer" and "Intersection" within the "Geometry by expression" from the Processing Toolbox (Ctrl+Alt+T).

Let's assume we have five features in 'poly_test' (purplish) and ten in 'random_points_test' (orange) accordingly, see image below.

In the "Geometry by expression" window use this formula in the 'Geometry expression' field:

intersection(geom_from_wkt(
                array_to_string(
                    overlay_intersects(layer:='poly_test', expression:=geom_to_wkt($geometry))
                    )
                ),
             buffer($geometry, 150000, 50)
        )

for creating buffers that do not exceed the boundary of polygons .

Press Run and get the output

Answer 3

There is a possibility using a "Virtual Layer" through Layer > Add Layer > Add/Edit Virtual Layer...

Let's assume we have five features in 'poly_test' (purplish) and ten in 'random_points_test' (orange) accordingly, see image below.

With the following query, it is possible to create buffers that do not exceed the boundary of some polygons.

SELECT poi.id,
       st_intersection(st_buffer(poi.geometry, 150000), poly.geometry) AS geom
FROM "random_points_test" AS poi
INNER JOIN "poly_test" AS poly ON st_within(poi.geometry, poly.geometry)

The output polygon layer (orange) with its attribute table will look like