<div dir="ltr" gmail_original="1"><div>A native QGIS solution based on Richard's query. With your union layer of 12 features, use the Processing Toolbox → Vector Geometry → Aggregate tool which offers a group by (geometry) and concatenate (by attribute) options to dissolve features. Screenshot below of the setting that produces 7 polygons with the desired names.</div><div><br></div><div><img data-surl="cid:01fa07fa-8f64-420a-8694-a737509048d7" src="cid:01fa07fa-8f64-420a-8694-a737509048d7" alt="union.png" width="495" height="369"><br></div><div><div dir="ltr" class="gmail_signature"><div dir="ltr">---<div>Ujaval Gandhi</div><div>Spatial Thoughts</div><div><a href="http://www.spatialthoughts.com" target="_blank">www.spatialthoughts.com</a></div><div><br></div></div></div></div><br></div><br><div class="gmail_quote gmail_quote_container"><div dir="ltr" class="gmail_attr">On Tue, Feb 17, 2026 at 9:51 PM Richard Greenwood via QGIS-User <qgis-user@lists.osgeo.org> wrote:<br></div><blockquote class="gmail_quote" style="margin: 0px 0px 0px 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;"><div dir="ltr">Here's another postgis solution. I started with your original QGIS union which has 12 polygons. Then in postgis:<blockquote style="margin: 0px 0px 0px 40px; border: none; padding: 0px;"><div><font face="monospace">select st_union(geom) as unique_geom, string_agg(attrib, ',') as concatenated_attribute</font></div><div><font face="monospace">from test </font></div><div><font face="monospace">group by geom;</font></div></blockquote>This is an aggregate query the groups by geometry. The "magic" is the string_agg function which concatenates the "attribute" field. The query produces 7 rows (below). The string_agg() function also accepts an ORDER BY if that's important to you.<div><img src="cid:f486aaae-fecb-4b38-b060-0eba56fbfe7a" alt="image.png" width="495" height="437" data-surl="cid:f486aaae-fecb-4b38-b060-0eba56fbfe7a"><br></div><div><div><br></div><div><br><div><br></div></div></div></div><br><img width="0" height="0" class="mailtrack-img" alt="" style="display:flex" src="https://mailtrack.io/trace/mail/w/cWdpcy11c2VyQGxpc3RzLm9zZ2VvLm9yZw/8827c79353d136f51fda245f31d084cec62dd69a.png?u=8747767" ><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Tue, Feb 17, 2026 at 8:23 AM Karl Magnus Jönsson via QGIS-User <<a href="mailto:qgis-user@lists.osgeo.org" target="_blank">qgis-user@lists.osgeo.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin: 0px 0px 0px 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;"><div>
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<p class="MsoNormal"><span style="font-size: 11pt;">Hi Simon!<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size: 11pt;">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.<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size: 11pt;"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size: 11pt;">WITH orings AS (<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size: 11pt;"> SELECT st_exteriorring((st_dumprings(<wbr>(st_dump(omr.geom)).geom)).<wbr>geom) AS geom<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size: 11pt;"> FROM qdp2.omr<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size: 11pt;"> ), oboundaries AS (<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size: 11pt;"> SELECT st_union(orings.geom) AS geom<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size: 11pt;"> FROM orings<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size: 11pt;"> ), opoly AS (<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size: 11pt;"> SELECT (st_dump(st_polygonize(<wbr>oboundaries.geom))).geom AS geom<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size: 11pt;"> FROM oboundaries<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size: 11pt;"> )<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size: 11pt;">SELECT row_number() OVER () AS id,<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size: 11pt;"> </span><span style="font-size: 11pt;">p.namn,<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size: 11pt;"> 'delområde'::text AS delomr,<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size: 11pt;"> </span><span lang="EN-GB" style="font-size: 11pt;">p.plan_uuid,<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size: 11pt;"> p.status,<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size: 11pt;"> p.publicerad,<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size: 11pt;"> op.geom<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size: 11pt;"> FROM opoly op,<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size: 11pt;"> qdp2.plan_omr po,<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size: 11pt;"> qdp2.plan p<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size: 11pt;"> WHERE st_contains(po.geom, st_pointonsurface(op.geom)) AND po.plan_uuid = p.plan_uuid<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size: 11pt;"><u></u> <u></u></span></p>
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<p class="MsoNormal"><span style="font-size: 10pt; font-family: "Franklin Gothic Book", sans-serif; color: black;">Med vänliga hälsningar<u></u><u></u></span></p>
<p class="MsoNormal"><b><span style="font-size: 10pt; font-family: "Franklin Gothic Book", sans-serif; color: black;"><u></u> <u></u></span></b></p>
<p class="MsoNormal"><b><span style="font-size: 10pt; font-family: "Franklin Gothic Book", sans-serif; color: black;">Karl-Magnus Jönsson</span></b><span style="font-size: 11pt;"><u></u><u></u></span></p>
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<p class="MsoNormal"><span style="font-size: 11pt;"><u></u> <u></u></span></p>
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<div style="border-right: none; border-bottom: none; border-left: none; border-top: 1pt solid rgb(225, 225, 225); padding: 3pt 0cm 0cm;">
<p class="MsoNormal"><b><span style="font-size: 11pt; font-family: Calibri, sans-serif;">Från:</span></b><span style="font-size: 11pt; font-family: Calibri, sans-serif;"> QGIS-User
<<a href="mailto:qgis-user-bounces@lists.osgeo.org" target="_blank">qgis-user-bounces@lists.<wbr>osgeo.org</a>> <b>För </b>Simon Dietmann via QGIS-User<br>
<b>Skickat:</b> den 17 februari 2026 15:01<br>
<b>Till:</b> qgis-user <<a href="mailto:qgis-user@lists.osgeo.org" target="_blank">qgis-user@lists.osgeo.org</a>><br>
<b>Ämne:</b> [Qgis-user] aggregate polygon overlay<u></u><u></u></span></p>
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<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal"><span lang="DE">Dear list,<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="DE"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB">I am trying to solve the following problem:<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB"><u></u> <u></u></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:<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB"><img width="406" height="387" style="width: 4.2291in; height: 4.0312in;" id="m_-7553186243197803901m_4770716411992134382Grafik_x0020_1" src="cid:5ed6d487-dfe1-4da5-a6c4-2b74816c6b46" data-surl="cid:5ed6d487-dfe1-4da5-a6c4-2b74816c6b46"></span><span lang="EN-GB"><u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB"><u></u> <u></u></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.<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB"><u></u> <u></u></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.<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB"><u></u> <u></u></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?<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB">Thank you for any hints,<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB">regards<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB">Simon<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB"><u></u> <u></u></span></p>
<p><span lang="DE" style="font-size: 10pt; 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"><u></u><u></u></span></p>
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</div></blockquote></div><div><br clear="all"></div><div><br></div><span class="gmail_signature_prefix">-- </span><br><div dir="ltr" class="gmail_signature"><div dir="ltr">Richard W. Greenwood<br></div></div>
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