Create a buffer for polygons that meet a condition with QGIS

Question

I have a layer with polygons, and I want to make a buffer but only for the ones that meet a condition ("MUNICIPIO"=5). When I make a fixed distance buffer, it makes a buffer for all the polygons in the layer. Is there a way to make a buffer only for the polygons I want?

Answer 1

Use Select by Expression from the attribute table to select polygons of "MUNICIPIO"=5 and use Fixed Distance Buffer for the selected polygons.

Use Fixed Distance Buffer from SAGA tools which you can find it from Processing toolbox -> SAGA -> Vector General tools -> Fixed Distance Buffer. It should work.

Make sure that Use only selected features option is checked from the Processing Option. It should be checked by default.

Answer 2

For this you can use a Virtual Layer.

Choose Add/Edit Virtual Layer in the Manage Layers Toolbar, import your layer and use a query like:

SELECT ST_Buffer(geometry, 100) FROM your_layer WHERE MUNICIPIO=5