Selection by location with distance parameter using QGIS

Question

I want to perform a selection by locatin in QGIS using "intersection." However, I want to add a distance parameter so that it disregards polygons that are exactly adjacent and retrieves only those that are at a certain distance.

To illustrate my example: I have a layer of communes of France (red shapefile). I want to select only the communes (green layer) that are within the shape of the Languedoc-Roussillon region (black outline).

If I perform a selection by location using intersection in QGIS, it will select all communes within (green layer), but also those that touch the boundary (yellow communes).

In ArcGIS, we can specify a distance parameter in the selection. In the case of my example above, I set it to "-10" to exclude the communes that touch the boundary. (Sorry, the menu is in French)

In QGIS, there is no way to add a parameter in the selection menu...

Answer 1

Try using the "Extract by expression" algorithm, the expression could be this one:

with_variable(
    name:='buffered',
    value:=buffer(
        $geometry,
        -10 -- set here the distance to filter features, this distance is in map units
    ),
    expression:=aggregate(
        layer:='Polygon layer name/id', -- put inside quotes the layer name/id that is going to filter the polygons
        aggregate:='count',
        expression:=1,
        filter:=intersects(
             $geometry,
             @buffered 
        )
    )
)

Answer 2

You can use the tool selectwithindistance

Just search for it in the Toolbox. You can open the Toolbox with strg + alt + t

Answer 3

For solving your particular problem, rather than negative buffering, an alternative approach is to consider the commune polygons as points.

By using pole_of_inaccessibility, you can treat the commune polygons to points with confidence that the point is inside the commune polygon (and hence inside your region polygon).

You need to supply the LayerId, Attribute, and Value for the Languedoc region, and Tolerance based on your units (1m or 0.000001 degree should be fine). Expression is of the form:

contains(
   geometry(
      get_feature(<LayerId>,<Attribute>,<Value)
   ),
   pole_of_inaccessibility($geometry,<Tolerance>)
)

Here's a specific example using districts in India. The points are just for visualisation.

contains(
   geometry(
      get_feature('IND_adm2_f8a55c74_b2be_45a5_9a48_e701942c7c5d','NAME_2','Anantapur')
   ),
   pole_of_inaccessibility($geometry,0.000001)
)

Answer 4

Use Select by expression with this expression and replace region_layer with your layer name:

within (
    $geometry, 
    overlay_nearest ('region_layer', buffer($geometry,0.1))[0]
)

The expression looks for each commune if it is completely within the nearest feature from the region_layer. For exact matches add a very small buffer around the region. This does not affect neighboring communes being selected, as we only select if a commune is completely within the region (not not just overlaps in the margins).

Screenshot: only those of the red polygons are selected (highlighted in yellow) that are completely within the blue polygon: