[Qgis-user] Problem Noticed with QGIS

[Richard McDonnell]

Andrea,
Thank you for the clarification and the work around!
Regards,

Richard



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Richard McDonnell MSc GIS, FME Certified Professional
FRM Data Management

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MSc GIS, FME Certified Professional

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Oifig na nOibreacha Poiblí
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Sráid Jonathan Swift, Baile Átha Troim, Co na Mí, C15 NX36
Jonathan Swift Street, Trim, Co Meath, C15 NX36
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M +353 87 688 5964 T +353 46 942 2409
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From: Qgis-user <qgis-user-bounces at lists.osgeo.org> On Behalf Of Andrea Giudiceandrea via Qgis-user
Sent: 29 November 2022 16:14
To: qgis-user at lists.osgeo.org
Subject: Re: [Qgis-user] Problem Noticed with QGIS

Richard McDonnell richard.mcdonnell at opw.ie<mailto:qgis-user%40lists.osgeo.org?Subject=Re%3A%20%5BQgis-user%5D%20Problem%20Noticed%20with%20QGIS&In-Reply-To=%3C9708d6dac99943929281a173e54a9e6f%40opw.ie%3E>
Tue Nov 29 07:17:48 PST 2022
________________________________

1.       If I use the option [Create temporary Layer] it produces a Singlepart Geometry as Expected, If I save the output to a File, the resultant geometry is stated as Polygon (MultiPolygon) Its the same for Linestrings also.

Hi Richard,
as explained (also by me) in the linked issue report [1], the line (PolyLine) and polygon (Polygon) ESRI Shapefile layer types are actually multi-part layer types which can store both multi-part geometries with only one part and multi-part geometries with more than one part.
Only the point layer type has two different ESRI Shapefile layer types: the ESRI Shapefile Point type (which is a single-part type and can store only single-part geometries) and the ESRI Shapefile MultiPoint type (which is a multi-part type and can store multi-part geometries both with only one part and with more than one part).

Please see the ESRI Shapefile Technical Description [2].

If you want to check that a line (PolyLine) and polygon (Polygon) ESRI Shapefile layer imported in QGIS contains features with only 1 part, you need to check the number of part for each feature, for example using the num_geometries function [3] in the field calculator.

Best regards.

Andrea Giudiceandrea

[1] https://github.com/qgis/QGIS/issues/50720
[2] https://www.esri.com/Library/Whitepapers/Pdfs/Shapefile.pdf/
[3] https://docs.qgis.org/3.22/en/docs/user_manual/expressions/functions_list.html#num-geometries
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