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My project has just over 100 layers, necessary for background reference info and all turned off until I need them. The overall task is to create a polygon layer that draws together information from multiple sources, adds professional assessments/scores and corrects for errors in the base data (everything from typos to broken geometry). It is a normal QGZ with no database etc. Plugins are minimal and I've tried turning them all off/uninstalling/using an alternate "clean" profile. Running QGIS 3.28.1

Editing consists of moving vertices around, creating new polygons, and adding and changing attribute data manually and by query. I make regular saves along the way of both the layer edits and the project. At some point around an hour in, I start to get problems. The attribute data will start to get "jumbled" i.e., the right attributes coming up for the wrong polygons. Also, vertices will start jumping around, snapping to seemingly random coordinates or a vertex on another polygon miles away (I have all layers layer vertex snapping on, tolerance 12px).

I will also get an annoying box overlaying the attribute table that contains the last value I input to the first field in the layer. It covers the actual value in field 1, row 1.

GUI input masking actual value

Is there anything I can do to stop this from happening or do I really just need to trim down my layers?

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  • If you close the project and then reopen it does that fix things for another hour or so or do you have to reboot? Are any of your layers WMS/WMTS? I'm just wondering if your rendering or WMS cache is filling up. If layers are on a network or involve some WMS layers that are slow, that can slow redraws. Houska's suggestions are worth trying. I'll note on snapping in addition to limiting what layers are involved at any time, if you have a layer with many vertices you might simplify it if possible or zoom in for your work to limit the vertices it has to track.
    – John
    May 12, 2023 at 20:39
  • Closing and restarting does fix some things temporarily but not consistently. My main base map is a WMS (google hybrid map). Zooming doesn't seem to affect the likelihood of a glitch.
    – Swordnut
    May 15, 2023 at 11:46

1 Answer 1

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While I do not recognize/experience the specific issues you are experiencing, some thoughts:

  1. Make sure you are running the latest version. At the time of your question (and this answer), the current LTR version is 3.28.6 for the LTR and 3.30.2 for the latest release. It's recommended to update to one of these, since bugs do get fixed as versions get released. [This point has been edited: when I first wrote it, Q read version 3.81 which I assumed meant 3.18; user has now clarified they meant 3.28 so they're fine but others in similar situation may not be.]

  2. 100 layers is a lot, is there any way to reduce the number of layers permanently part of the project? It is pretty easy to bring in layers ad-hoc when you need them using the Browser. You can either just open them from wherever they are stored, or by creating and then from the Browser opening up a separate "data index" project where you have all your layers (and associated formatting etc) referenced but not do editing/analysis, and dragging them into your main project when needed. Doing this has improved performance for me with many layers; I haven't had stability issues like you but might help in that regard.

  3. You seem to have snap to vertices, all layers, turned on. If you have many vector layers, this might impose a significant performance penalty. Can you select a subset of the layers to snap to?

  4. It is possible for some of the settings in a layers file to become corrupted, and I would expect the chances increase with many, many layers. So especially if you would be pruning down the loaded layers, it might be a good idea to restart the project from scratch, reload layers one at a time or in small groups, to try to eliminate any possible corruption. Painstaking, I know, but an idea.

  5. Finally, a shot in the dark. I have been amazed how in some of my projects, "ghost layers" (mentioned in the XML in the project but no longer in the legend, e.g. deleted) show up. The https://plugins.qgis.org/plugins/LayerBoard/ plugin allows removing such ghost layers. While I see no particular reason this should be your issue, it could be a easy thing to try to see if it resolves your problems, especially if your current 100 layers are the accretion of even more layers being added, edited, removed, readded, etc.

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  • Thanks, 1 - its 3.28.1, Ive corrected the typo. 2 - I have cut the layers right down in a new project now as well as increasing the system cache size to 1GB. Still getting the GUI problem but less of a problem with vertices. 3 - I have set up a custom snapping profile now. 4 - I will see how it goes and if there is a problem as I add layers back in, Ill do as you recommend. 5 - Thanks, Ill try that as well. Will need time to get back to the project for a long session before I know if anything is fixed.
    – Swordnut
    May 15, 2023 at 12:02

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