In a heat island effect control project, I start from two point layers with the values of daytime and nighttime temperatures in degrees C:



These layers contain the "TEMP" field with the temperature values. I add an example screenshot:

enter image description here

I would like to calculate the temperature difference between Day and Night Temperature with the each nearest points where the measurements have been captured.

I use a Geometry Generator expression to visualize each nearest point of the POINTS_DAY layer to the POINTS_NIGHT layer by connecting the two points with a line. I achieve this with the following expression for Geometry Generator:

collect_geometries (
    array_foreach (
        overlay_nearest (
            'target_p', -- rename the layer if necessary
        make_line (

enter image description here

My goal is to calculate the temperature substraction between each pair of nearby points, and fill the "DIFF" field of the POINTS_DAY layer with the substraction value.

1 Answer 1


We can do this with an update expression on the "DIFF" Field of the POINTS_DAY layer as follows:

TEMP - overlay_nearest(layer:='POINTS_NIGHT', expression:= TEMP, max_distance:= 500)[0]

i.e. Temperature value [TEMP] for the current day point minus [-] the temperature value [TEMP] for the nearest night point ['POINTS_NIGHT'] within 500 metres/units.

You can change the 500 to increase the search areas for the closest point.

Nearest Point Difference Value Expression

Nearest Point Difference Value

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