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<p class="MsoNormal"><span style="font-size:11.0pt">Hi Simon!<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt">Seems like a common problem that GIS should handle easy, but it is perhaps not that easy. I had a similar problem that ended up in below. I have my data in Postgres + PostGIS so it is handled
by the database in in a view. The code disassembles the polygons in the rings, union the rings and then build polygons again from the lines. Then I do a join with the original data (in this case not exactly) based on location on the centerpoint. In your case
I would do a suitable group by and concatenate the attributes. Hope this helps even it is not QGIS.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt">WITH orings AS (<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt"> SELECT st_exteriorring((st_dumprings((st_dump(omr.geom)).geom)).geom) AS geom<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt"> FROM qdp2.omr<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt"> ), oboundaries AS (<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt"> SELECT st_union(orings.geom) AS geom<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt"> FROM orings<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt"> ), opoly AS (<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt"> SELECT (st_dump(st_polygonize(oboundaries.geom))).geom AS geom<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt"> FROM oboundaries<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt"> )<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt">SELECT row_number() OVER () AS id,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt"> </span><span style="font-size:11.0pt">p.namn,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"> 'delområde'::text AS delomr,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"> </span><span lang="EN-GB" style="font-size:11.0pt">p.plan_uuid,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt"> p.status,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt"> p.publicerad,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt"> op.geom<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt"> FROM opoly op,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt"> qdp2.plan_omr po,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt"> qdp2.plan p<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt"> WHERE st_contains(po.geom, st_pointonsurface(op.geom)) AND po.plan_uuid = p.plan_uuid<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Franklin Gothic Book",sans-serif;color:black;mso-ligatures:none;mso-fareast-language:SV">Med vänliga hälsningar<o:p></o:p></span></p>
<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Franklin Gothic Book",sans-serif;color:black;mso-ligatures:none;mso-fareast-language:SV"><o:p> </o:p></span></b></p>
<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Franklin Gothic Book",sans-serif;color:black;mso-ligatures:none;mso-fareast-language:SV">Karl-Magnus Jönsson</span></b><span style="font-size:11.0pt;mso-fareast-language:SV"><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-ligatures:none;mso-fareast-language:SV">Från:</span></b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-ligatures:none;mso-fareast-language:SV"> QGIS-User
<qgis-user-bounces@lists.osgeo.org> <b>För </b>Simon Dietmann via QGIS-User<br>
<b>Skickat:</b> den 17 februari 2026 15:01<br>
<b>Till:</b> qgis-user <qgis-user@lists.osgeo.org><br>
<b>Ämne:</b> [Qgis-user] aggregate polygon overlay<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span lang="DE">Dear list,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="DE"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">I am trying to solve the following problem:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">I have one polygon layer with many polygons that are in many cases overlapping and with different attribute valus, e.g. a, b, c:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="mso-ligatures:none"><img width="406" height="387" style="width:4.2291in;height:4.0312in" id="Grafik_x0020_1" src="cid:image001.png@01DCA028.5EA7E630"></span><span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">My goal is to generate a polygon layer with polygons for every overlap constellation containing a concat string of those attributes, in this example seven polygons with the attributes a, b, c, ab, bc, ac, abc.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">I started with a union of my original layer, the result is a layer with 12 polygons where overlapping areas of the original polygons result in overlapping intersections containing one of the original attributes each,
for example in the middle, there are 3 polygons, one with a, one with b and one with c.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">How is it possible to summarize those overlapping polygons into one polygon each with all the attributes, given that there is a large number of polygons and different attributes?<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Thank you for any hints,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">regards<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Simon<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p><span lang="DE" style="font-size:10.0pt;font-family:"Arial",sans-serif;color:black">i.A. Simon Dietmann<br>
Projektleiter | Geograph</span><span lang="DE" style="font-family:"Arial",sans-serif;color:black"><br>
<br>
</span><span lang="DE"><o:p></o:p></span></p>
<p><span lang="DE"><img width="204" height="89" style="width:2.125in;height:.927in" id="Bild_x0020_2" src="cid:image002.png@01DCA028.5EA7E630"></span><span lang="DE"><o:p></o:p></span></p>
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