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

[Emma Hain]

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: 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
[image: https://north-road.com]
*North Road*
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