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I have a set of points (one to many) in polygon. The middle polygon has a lot of concentrated and correlated points. Looking to see if there is way or an algorithm within QGIS to reduce the number of points, for lack of a better word reverse interpolations.

enter image description here

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  • How do you decide there is too many points? Why is this causing a problem? You could use some sort of cluster grouping but without knowing your data intimately I cannot guide on how to reduce the number of points - what are the points? How does one point become less or more important than the others?
    – Michael Stimson
    Commented Mar 22, 2017 at 0:15
  • Thanks for your reply. The above vector is a polygon with point representing pizza restaurants. Is there a way in qgis i can group cluster and more of less consolidate,
    – user93905
    Commented Mar 22, 2017 at 0:34
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    I would buffer by a small amount, perhaps 1km or 1 mile, the exact number would depend on your data on a trial and error basis, dissolve the polygons and then use the centroids as points.. any instances closer than 2xbuffer become one... be careful though, you can easily over simplify using this method. As each one is weighted the same there is no way to promote or discard. You could intersect the points with the buffer before extracting centroids to obtain the count of points so you can later show the number of individual records the points represent.
    – Michael Stimson
    Commented Mar 22, 2017 at 0:42
  • gis.stackexchange.com/questions/159285/…
    – bcollins
    Commented Mar 22, 2017 at 2:26
  • Do you want it only for visualisations? Then check the Rendering tab of Layer Properties.
    – pnz1337
    Commented Apr 11, 2018 at 15:07

1 Answer 1

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You could try the SAGA tool named Points thinning which is accessible in QGIS Processing Toolbox | SAGA | Vector point tools | Points thinning.

A picture below shows (a) randomly distributed (100) green points , which then (b) be reduced to (48) red points by Points thinnging tool.

There is a parameter to be set, Resolution (default value: 1.0). In this example I set Resolution to 500. The meaning of this Resolution will be understood looking at (c) green circles (250m radius) underlying the thinned red points.

enter image description here

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    Looking at image (c), in both the bottom left and bottom right corners, there are points that overlap the buffers showing that Points thinning is not doing what I might expect in regards to the 500m resolution (It’s not respecting the 250m buffer). I’m guessing this has to do with those points being isolated and perhaps the density is still within the parameter because those points aren’t close to other points. Is this correct?
    – aiwetir
    Commented Dec 13, 2019 at 8:22

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