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I have shapefiles of sea ice coverage for multiple days of the year. At each time-point (day) the sea ice is split into different polygons which corresponds to different ice types (i.e. fast ice, consolidated ice, etc). I have four coordinate points and I would like to obtain the frequency or the counts of the different polygon types occurring at those specific coordinates along the whole year.

Is there a way to do this in QGIS?

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    Possibly a duplicate of this question
    – Fee
    Dec 2, 2020 at 14:21
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    Please clarify what's in each shapefile. Is it one shapefile per day? Or maybe one shapefile for the whole year for a specific region? Something else?
    – Llaves
    Dec 2, 2020 at 15:47
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    I think this question is sufficiently different from the one identified above that I would recommend against closing.
    – Llaves
    Dec 2, 2020 at 15:51
  • Hi @Llaves, originally I received one single shapefile for each year which, for each day, had the different polygons. Since I did not know how to work with the file all lumped together I split it in different layers for each day with the "Split Vector Layer". So I have both files, all days together in one single shapefile with two classes "date" and "ice type" or each day as a single shapefile. For each day there are 6 different types of ice or polygons, although not all polygons appear in all days since there are some days of ice free conditions. It's just for a specific region. Dec 3, 2020 at 8:46
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    can you share the all-year shapefile, or perhaps a few days worth (if it's large)? I think a spatial join might be a viable approach, but hard to tell without seeing the data
    – Llaves
    Dec 3, 2020 at 16:26

1 Answer 1

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This approach is probably tedious -- not recommended if there is another way.

(1) "Split Vector Layer" tool to split the original layer to 6 layers as per the type of ice.

(2) Run Union tool (in the Processing Toolbox > Vector geometry) to divide polygons at overlaps.

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(3) This returns a new layer 'Union'. As the attribute table of 'Union' shows only the original polygon id, we need to calculate counts by an expression count("id", group_by:= geom_to_wkt($geometry)).

enter image description here

(4) Lastly, activate Identify Features tool and click on your observation point to find the counts.

enter image description here

(5) Problem is, you have to repeat above process 6 times (for whole ice classes)... ...

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