[Qgis-user] Rendering shared exterior boundaries of adjacent polygon features

[Zoltan Szecsei]

Hi,
Also for clarification:
Being a County layer, I would not expect overlapping polygons.
My take is that Tim means "concurrent exterior boundaries" and not 
"overlapping exterior boundaries"

*Tim: *What is the reason for wanting only one of the concurrent(?) 
boundaries rendered?
Maybe there are other ways to do what you want to.

HTH,
Zoltan


On 2024/06/20 07:46, Emma Hain via QGIS-User wrote:
> Hi Tim
> So let's see if I understand you.
> - There are 2 polygon layers (green and black)
> - These polygon layers sometime overlap
> - You wish to show only on the pink line in the below image and not 
> the green overlapping part?
> image.png
>
>
> On Thu, 20 Jun 2024 at 11:26, Tim Malloy via QGIS-User 
> <qgis-user at lists.osgeo.org> wrote:
>
>     Fellow QGIS Users –
>
>     I’m trying to determine if its possible to have QGIS render the
>     exterior boundary of polygon features only once when that boundary
>     is shared with an adjacent feature (don’t render overlapping
>     exterior boundaries for both polygon features).The data I’m
>     working with is a county parcels layer and the symbology I’m using
>     for this layer is a cross hatched line fill with a separate
>     component for the outline of the polygons.I’ve tried a couple of
>     expressions (examples below) including one geometry generator and
>     one data defined override for the stroke width of the boundary
>     line but none of them achieves my objective.I’m using QGIS 3.34.7
>     and my coding skills are limited.I feel like I’ve seen this issue
>     covered somewhere but have been unable to find a solution after
>     extensive online exploration.
>
>     *Method #1:“*boundary( difference( $geometry, aggregate( 'union',
>     'intersects', $geometry, other_layer := @layer)))”This expression
>     was used on the outline component of the symbology described above.
>
>     *Method #2:*“CASE WHEN intersects( $geometry, geom_to_wkt(
>     boundary( $geometry ))) THEN 0 ELSE 1 END”Here I switched to using
>     an expression on the stroke width of a simple fill, but I got an
>     error message saying “Cannot convert to geometry”.
>
>     Any input would be greatly appreciated.
>
>     Tim
>
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>
> -- 
> Emma Hain — Product Manager/Senior GIS Analyst
> emma at north-road.com
> https://north-road.com
> 	*North Road*
> Cartography • Development • Spatial Analysis
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-- 

=============================================
Zoltan Szecsei GPrGISc 0031
Director, Geograph (Pty) Ltd.
GIS and Photogrammetric Services

Cape Town, South Africa.

Mobile: +27-83-6004028 (Signal, not WhatsApp)
         +974-5058-8729
         +36-20-4808362

www.geograph.co.za
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