QGIS Select by Location – Selecting Points Within One Polygon in a Different Layer

qgisselectselect-by-attributeselect-by-expressionselect-by-location

I have a set of points, which are located in the same area where the other, polygon layer is located.

I would like to have all the points selected, but ONLY within the one polygon belonging to the different layer. I.e. I would lie to have all points selected within the Polygon ID = 1 and so forth.

The following option:
Vector -> Research Tool -> Select by location -> "Are within"
simply doesn't work, because it selects the points falling within the whole polygon layer, which comproses of 7 polygons exactly. I would like to have the selection only within one polygon.

I think, the issue could be an analog to this thread:

Selecting only polygons that contain another polygon with Select by Location in QGIS

However, these formulae applies didn't work.

Potentially this option:

points within a polygon

could be doable, but it looks like I have to create some virtual layer first.

I tried also these approaches:

Intersection between points and polygons in QGIS

QGIS select by location doesn't use selected features only

https://www.youtube.com/watch?v=CU1A86JJMIk&ab_channel=OpenSourceOptions

Selecting features within polygon from another layer using QGIS

QGIS how to select entries not in another layer

but they didn't work for me.

Is there any way to make this selection just within one polygon of the external layer?

Best Answer

If you check "Select features only" option for the polygon layer, you can select the points within the selected polygon.

Related Solutions

[GIS] Selecting features within polygon from another layer using QGIS

Two possible solutions:

You can use the "Select by Location" from Vector > Research tools > Select by Location and tick the "Use selected features only" checkbox.
If you want to actually export the points which intersect your selected polygon to a new shapefile then "Intersection" from Vector > Geopressing tools > Intersection and again tick the "Use only selected features" checkbox. The input layer will be your points layer, and the select layer will be your polygon layer.

[GIS] Debugging Select By Attribute tool within loop giving ERROR 000358: Invalid expression Cannot acquire a lock

Give this a try:

where="map_name = '%s'" % (map)

Also on your get count line, if DI_Count is an Integer field - change it to something like this:

count = int(arcpy.GetCount_management(ds).getCount(0))

I looks like you are wanting to select all the points within each treatment area and get a count and populate that treatment area with the point count? correct? If this is true, try the following:

# treatment_maps_ds - this is the name of your input polygon dataset
treatment_area_list = [row.map_name for row in arcpy.SearchCursor(treatment_maps_ds)]
# point_ds - this is the name of your input point dataset
arcpy.MakeFeatureLayer_management(point_ds, "ptslyr")
arcpy.MakeFeatureLayer_management(treatment_map_ds, "treatmentlyr")

# Loops through each treatment 'map_name'
treatdict = {}
for treatmap in treatment_area_list:
    arcpy.SelectLayerByAttribute_management("treatmentlyr", "NEW_SELECTION", "map_name = '" + str(treatmap) + "'")
    arcpy.SelectLayerByLocation_management("pntlyr", "INTERSECTS", "", "treatmentlyr")
    cnt = int(arcpy.GetCount_management("pntlyr").getOutput(0))
    treatdict[treatmap] = cnt

cur,row = None, None
cur = arcpy.UpdateCursor(treatment_maps_ds)
for row in cur:
    cnt = treatdict[row.map_name]
    row.DI_Count = cnt
    cur.updateRow(row)

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