QGIS Heatmap – How to Create Series of Annual Heatmaps in QGIS

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I'm working with QGIS 3.22.10-Białowieża and I've got a point layer with the attribute year. I need to create a series of heatmaps, one for each year, but I haven't found any filtering option in the heatmapkerneldensity tool (or any other) to perform such an iteration.

Is there an automatic way of doing so?

Best Answer

You can automate the task:

Create a model for your workflow (find the model I created for this task here to download)
Run your model in batch mode, running it once for each year you wish.

Create model

Create a model I linked above with 2 inputs: point layer and numer for year to be selected. Then add Extract by expression algorithm. For expression, choose year = @year_selected (change this to attribute name and model input name you have):

Run model in batch mode

Run your model and choose batch mode. For year selected, use Autofill... and select add values by expression. Create an array that contains all years for which you want to generate a heatmap. For years 2015 to 2022, I used: generate_series(2015,2022).

For input point layer and heatmap (output), fill in the first row and than choose Fill down. When you do this for the output, you will be promted for autofill mode: select Fill with parameter values and select year_selected to get the year added to the file name:

Related Solutions

[GIS] Using polygons to create heatmaps in QGIS

You might want to create centroids for your grid of polygons, then and attach the weight value of the data with no exact location (located in a grid cell) to the centroids. This can be accomplished by:

Vector->Geometry Tools->Polygon centroids
Vector->Database management->Join attributes by location

That should give you the weights (from each polygon in the grid) into a point layer of centroids. Now you can merge these points together with your actual point locations to create one point vector with weights, and do any further heat maps etc.

If you want to total the weight per polygon, that's an additional process. I do these kinds of things in a database. Import both the polygon grid and the points into Spatialite, for example then try these SQL commands in Spatialite-gui:

ALTER TABLE grid ADD COLUMN total_weights REAL;
UPDATE grid SET total_weights=(SELECT SUM(p.weight) FROM points AS p WHERE ST_Contains(grid.geometry, p.geometry));

(Of course, you'll have to adjust the column names and table names)

[GIS] Zonal Statistics for multiple rasters

I have something fairly close, although it only currently works for average and rejects max and min.

Save all your raster layers in one folder with the same extension (e.g. .tif)
Load shapefile (polygons) into QGIS

Open Python (Plugins > Python console) and run the following

import glob, os, qgis.analysis
vectorlayer = qgis.utils.iface.mapCanvas().currentLayer()
rasterfolder = 'C:/Users/…/Folder/'
os.chdir(rasterfolder)
for lyr in glob.glob("*.tif"):
    qgis.analysis.QgsZonalStatistics(vectorlayer, lyr, attributePrefix=lyr, rasterBand=1).calculateStatistics(None)

Using the vector layer loaded in QGIS was an easy way to append the results to the attribute table. The code to loop through rasters in a folder was from here.

If there is a way to specify the statistic using QgsZonalStatistics.Mean that would be helpful to know.