QGIS – How to Label Point Layer with Percentage of Points in Polygon Layer

countgeometry-generatorpointqgis

I would like to find a method using Geometry generator to label a point layer with the percentage of points inside another polygons layer.

I'm working on implementing a solution based on the COUNT and OVERLAY_WITHIN functions, but for the moment I can't get the solution. An approach of my failed expression is this:

count(within($geometry,collect_geometries(overlay_within('POLYGON', $geometry))))*100/num_geometries($geometry)

With this result:

The idea I am looking for is as shown in the screenshot: label point layer in the centroid of each polygon with the percentage of points:

Best Answer

From what you say, it seems like you wanted to start from the points layer. As you want the number of points within the polygon layer, it's easier to place the logic in the polygon layer (also allowing you to use the native label positioning features, centroid by default).

You can use this formula in the polygon layer Label (or as a Virtual Field in the polygon Attribute Table)

to_string(

   round(

         array_length(overlay_intersects('points', $id)) ---number of points in the polygon
         /
         aggregate('points','count',$id) ---number of points in points layer

   ,2)*100

) ||  ' %'

If you want this to automatically apply to any new Point layer, you can update the code to be the following :

  to_string(

   round(

         array_length(overlay_intersects(  array_to_string(  array_filter( @map_layer_ids ,@element!=@layer_id)), $id)) ---number of points in the polygon
         /
         aggregate(  array_to_string(  array_filter( @map_layer_ids ,@element!=@layer_id)),'count',$id) ---number of points in points layer

   ,2)*100

) ||  ' %'

with the point layer name replaced by array_to_string( array_filter( @map_layer_ids ,@element!=@layer_id)) which is the only active layer besides the polygon one. If there are other 'static' layers you want to exclude, you can add them to the filter.

Swithching to another point layer, without changing the Style in the polygon layer:

If you have static layers that you want to keep active: add them to the layer filter. Set the filter part to:

@element not in (@layer_id, 'any other layer name you need to remove', 'any other layer to remove',...)

`@layer_id' filters the polygon layer, then add a comma separated list of layers you want to keep active.

For instance I added an OtherLayer displayed on the map. Use the @map_layer_ids to identify its id and added it to the filter list

to_string(round(array_length(overlay_intersects( array_to_string( array_filter( @map_layer_ids ,@element not in (@layer_id,'OtherLayer_a9983d8b_9323_4fac_83de_e8e24e78c8a1'))), $id)) /aggregate( array_to_string( array_filter( @map_layer_ids ,@element not in (@layer_id,'OtherLayer_a9983d8b_9323_4fac_83de_e8e24e78c8a1'))),'count',$id) ,1)*100) || ' %'

Related Solutions

QGIS Labeling – How to Label the Percentage of Different Attributes

It can be achieved by aggregating the various values into arrays (using filters to choose the attribute value), then finding the length of those arrays.

-- this case statement is to ensure the label is rendered only once per group (else it is rendered for every feature)
case when $id = array_min(array_agg($id, group_by:="TYPE"))
then
-- get total count
with_variable(
    'total',
    array_length(
        array_agg($id)
    ),
    
    -- count how many instances of "Normal"
    with_variable(
        'normal',
        array_length(
            array_agg(
                "TYPE",
                filter:="TYPE"='Normal'
            )
        ),
        -- count how many instances of "Special"
        with_variable(
            'special',
            array_length(
                array_agg(
                    "TYPE",
                    filter:="TYPE"='Special'
                )
            ),

             -- generate the label string based on the value of "TYPE" ( || is the concatenator operator, the @ symbol is to call the variables that were created above)
             case 
                when "TYPE" = 'Normal'
                then 'Normal: '  || @normal  || ' (' || to_string(@normal / @total * 100) || '%)'
                when "TYPE" = 'Special'
                then 'Special: ' || @special || ' (' || to_string(@special / @total * 100) || '%)'
             end
                
        )
    )
)
end

The adapted placement expression:

case 
    when "TYPE" = 'Special'
    then
        point_on_surface(
            convex_hull(collect($geometry,filter:="TYPE"='Special'))
        )
    when "TYPE" = 'Normal'
    then 
        point_on_surface(
            convex_hull(collect($geometry,filter:="TYPE"='Normal'))
        )
end

QGIS – Drawing Line to Centroid of Concave Hull Composed by Group of Points in Same Polygon

The trick is to first collect the points within each polygon with the functions collect() and overlay_within(). Use this expression:

centroid (
    concave_hull( 
        collect(
            $geometry, 
            group_by:=overlay_within('POLY',$id)
        ),
        0.4
))

Red point created with the expression from above; red line: concave hull, created with the same expression, without the centroid() part:

To draw a line from the initial points to the centroid of the concave hull, simple add make_line ($geometry, at the beginning of the expression and add a closing bracket ) at the end of the expression, see:

Best Answer

Related Solutions

QGIS Labeling – How to Label the Percentage of Different Attributes

QGIS – Drawing Line to Centroid of Concave Hull Composed by Group of Points in Same Polygon

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