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I was going to delete all the QMD files but would like to know what they are for before I do in case there is a critical reason for the file(s) being produced. I know they contain Metadata but what for and why?

Vic
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When a layer is exported to any file based layer format (except GeoPackage), the layer metadata are saved in a *.qmd file if the Persist layer metadata checkbox is checked in the "Save Vector Layer as..." dialog window.

Andrea Giudiceandrea
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  • Thank you, that explains why the file is created but I’d be interested to know why you would tick or untick “Persist layer metadata”. – Vic Jun 26 '23 at 18:19
  • @Vic, probably I don't understand exactly your question... It seems to me the answer is obvious: if you want to store the layer metadata (see what are the layer metadata at https://docs.qgis.org/3.28/en/docs/user_manual/introduction/general_tools.html#metadata as already linked in the answer) to a file, you need the checkbox is ticked, otherwise not. – Andrea Giudiceandrea Jun 27 '23 at 06:39
  • I was trying to say "Why" would you want to store metadata separately? Also how would you use the qmd file? – Vic Jun 27 '23 at 09:54
  • @Vic, most of the layer formats cannot store the metadata, so they are normally stored in the QGIS project. If you export a layer that has associated metadata stored in the project and you want to also export such metadata, then you need to ensure the "Persist layer metadata" checkbox is ticked: the metadata associated to the layer will be saved to a .qmd file since most of the layer formats cannot store the metadata (except for the GeoPackage format which can store the metadata). The metadata saved in a .qmd file will be associated to the corresponding layer when imported in a QGIS project. – Andrea Giudiceandrea Jun 30 '23 at 12:32
  • Understand now. – Vic Jul 01 '23 at 19:31