QGIS – Selecting Only One Point within a Polygon

pointpoint-in-polygonpolygonqgisselect-by-location

I have two shapefiles: polygon(buffer) and point.

How can I select only one point in each buffer in QGIS?

If I use the "Select by Location", I will get all points inside the polygons, however I need only one? It doesn't matter which point out of two or more in polygon is selected.

Best Answer

If you don't care which point is selected, you can use this small PyQGIS script. Paste into a blank editor in the Python Console, change the layer names in the first two lines to match your layer names and click run.

# Change layer names in the first two lines to match your layers...
point_lyr = QgsProject.instance().mapLayersByName('New scratch layer')[0]
poly_lyr = QgsProject.instance().mapLayersByName('Buffered')[0]

ids = []

for feat in poly_lyr.getFeatures():
    contained_point = [f for f in point_lyr.getFeatures() if f.geometry().within(feat.geometry())][0]
    ids.append(contained_point.id())

point_lyr.selectByIds(ids)

Result:

Related Solutions

[GIS] Determining which polygon(s) each point lies in using QGIS

I solved this problem. Simply use the "Intersect" feature under Geoprocessing tools.

QGIS – How to Select Features Intersecting Another Layer’s Selection

VirtualLayers possibly to the first world problem rescue; this is a nice solution if you can express your polygon selection with some condition (I use an id <some_id> as an example here):

Layer -> Add Layer -> Add/Edit Virtual Layer...
Import -> both your WFS layers when loaded
(you can try adding the service directly via Add -> select WFS as provider and paste in the URL, but it keeps on throwing errors for me on QGIS 2.18)

and then type

SELECT pts.*
FROM <point_layer> AS pts,
     <polygon_layer> AS plg
WHERE plg.<id_column> = <some_id>
  AND ST_Intersects(pts.geometry, plg.geometry);

into the Query field.

If you want to manually select features:

Edit -> Copy Features
Edit -> Past Features As -> Temporary Scratch Layer...

and continue with your usual workflow from there
(you could of course use that layer in the above query to get the intersecting points into a virtual layer; just omit plg.<id_column> = <some_id> AND in above query and replace <polygon_layer> with the name of the scratch layer).

Best Answer

Related Solutions

[GIS] Determining which polygon(s) each point lies in using QGIS

QGIS – How to Select Features Intersecting Another Layer’s Selection

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