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I am working with QGIS to compute the annual burned area of my study area in Chile. I have two different layers.

  • One polygon layer which is a 1km x 1km grid of my study area. The only information this layer contains is a unique "id" for every grid cell.
  • The second layer is a point layer of fires. It contains information about the size, direction and duration of the fire. Every point is one fire. Multiple points (fires) can lie within a grid cell.

I now want to compute the average size of fires in each grid cell. How can that be accomplished?

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  • Step 1: Tell us which software you're working with.
    – Erik
    Nov 1, 2021 at 14:38
  • @Erik I edited the question. Nov 1, 2021 at 14:54

1 Answer 1

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This is an example trying to mimic your situation. Please modify layernames and field names according to your project.

enter image description here

Above figure shows two layers: Fire point layer with size field, and Grid layer with id field only.

Start Field Calculator on the Grid layer, and give this expression:

array_mean(overlay_contains('Fire', expression:= "size"))

enter image description here

It will return averaged fire size. (It returns null where you do not have any fire).

enter image description here

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  • Thank you. I found another way which is way more time consuming. That saves me a lot of time. A hint for other people: array_mean is only avabile since QGis 3.18. Nov 2, 2021 at 15:19

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