[Qgis-user] Problem Noticed with QGIS

[Andrea Giudiceandrea]

> *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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