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I have the following problem: I have a set of 27 "destinations" which I have selected manually and saved as a POINT layer. I have loaded several raster data layers into my project (with varying pixel sizes), and I would like to sum the raster values (for example pregnancy data) within a given radius around each of these 27 destination points, so that in the end I have the sum of annual pregnancies (for example) in a 3km radius around each of these predefined points.

What I have tried: I have used the "Buffer" tool, to create circles with a radius of 3km around each of these points, and have then used the "Rasterize (vector to raster)" tool to convert these circles to a raster layer. I then tried to use the "Raster layer zonal statistics" tool to get the data associated with each destination.

The problem is that since the result is a single raster layer, I cannot get the destination-specific data I was hoping for, just the sum total and mean of all annual pregnancies around all 27 destinations in my case.

How do I get around this problem?

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    What you need is Zonal statistics tool, not Raster layer zonal statistics. And you do not have to rasterize; just use your buffer (vector layer) as is.
    – Kazuhito
    Nov 2, 2021 at 11:24
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    Thank you!! I think that worked as intended - I was just manually checking the sum count, but you're right it bypasses the rasterization step
    – najusten
    Nov 2, 2021 at 11:54
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    Glad to know it worked. If you still want to work on Raster layer zonal statistics, you would need to rasterize the polygon according to each destination numbers (1, 2, ..., 27). I am afraid, when you rasterized the buffer layer, it might have had only one value such as 1. That's why I recommended Zonal statistics tool instead.
    – Kazuhito
    Nov 2, 2021 at 14:27
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    @Kazuhito, I think your comment(s) deserve to become a valid answer :)
    – Taras
    Nov 3, 2021 at 6:04
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    Thanks @Taras It may take a while for me to prepare an example to explain what (might) have happened, but will do definitely.
    – Kazuhito
    Nov 3, 2021 at 6:16

1 Answer 1

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This is a partial answer to try to explain Raster layer zonal statistics.

(1) An example of a raster layer and an overlying Buffer polygon layer.

enter image description here

(2) Rasterize the polygon; assign Destinations as the input field. (To rasterize, I used SAGA > Raster - Rasterizing > Polygons to Raster tool).

enter image description here

(3) Start Raster layer zonal statistics tool.

enter image description here

(4) It will return Statistics table with area(m2), sum, cell count, min, max, mean values.

enter image description here

Using the tool itself is straghtforward, but the Rasterize step is tricky. Today I had problem with GDAL Rasterize (vector to raster) tool, which output layer is misplaced for whatever reasons...

Anyway, I would suggest Zonal statistics tool; as we can go without rasterizing task.

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