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I have many datapoints within 57 buffers in GIS (see picture for an example of a couple of the. buffers with datapoint inside). I need to be able to analyze each buffer separately, and therefore need a unique ID representing which data point comes from which buffer.

If I don't 'export by location' iteratively, and just have one layer with all the points extracted from the buffer, is there a way to make GIS attribute each datapoint with an ID that indicates which buffer that data point is within?

57 buffers

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  • As a new user, please take the Tour, which emphasizes the importance of asking One question per Question. Please Edit your Question to only ask one question.
    – Vince
    Aug 21 '21 at 17:33
  • You don't say what GIS system you are using! In ArcMap this would be the spatial Join tool.
    – Hornbydd
    Aug 21 '21 at 17:43
  • Apologies, it's QGIS. Aug 21 '21 at 17:57
  • Look at this tutorial.
    – Hornbydd
    Aug 21 '21 at 19:16
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On your datapoints layer (red in the screenshot below), create a new attribute with field calculator using this expression:

array_first (overlay_nearest('buffer',$id))

Replace buffer with the name of your buffer layer. Where two buffers overlap, you'll get the id of the "closer" one: the one with the nearest centroid.

Red datapoints labeled with the id of the buffer: enter image description here

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  • Thanks - this answer works, however I will be doing this in two separate layers, and when I try this method the buffer ID begins at "1" for both layers, when in reality I need the buffer IDs from the second layer to begin at "58" (as there are 57 buffers in the first layer). Is there a way I can alter the ID of this second layer? Aug 24 '21 at 14:28
  • Yes. You can create a new field with field calculator, give it a name (let's say id_new) and use the expreesion $id+57 to create the values. $id 1 will get a value of 58, $id 2 a value of 59 etc. Than in the expression from above, at the end replace $id with the name of the new attribute (like id_new in my case).
    – Babel
    Aug 24 '21 at 14:38
  • Thanks so much! Out of curiosity, in the "array_first (overlay_nearest('buffer',$id))" expression, where does the "$id" come from? Does QGIS automatically generate this id for each buffer, or is it based on the row number, or something else? Aug 24 '21 at 15:21
  • Yes, $id is automatically created for each feature - it's kind of numbering the features for identification purpose.
    – Babel
    Aug 24 '21 at 15:22

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